Description
This section documents keywords and options useful for developers who are extending and/or interfacing to Gaussian 16. It also discusses nonstandard routes and the determination of the standard orientation.
Keywords
The keywords and options described here are useful for developing new methods and other debugging purposes, but are not recommended for production level calculations.
General Job Restart
Restart
We discuss here the general use of Restart, designed for debugging. See the Restart section for production use. This keyword restarts a calculation by reusing the readwrite file. The form Restart L1 reuses the readwrite file but generates a new route.
Restarts using the original route can specify the occurrence of a particular link and whether to clean up or retain overlay and linkvolatile files using the following syntax:
#P Restart [Ln[(m)]] [CleanKeepOverlayKeepAll]
When all parameters are specified, the job restarts at the mth occurrence of Link n. Clean requests that all routine and overlay volatile files be removed by Link1, KeepOverlay requests that overlayvolatile files be retained but not linkvolatile ones, and KeepAll retains everything. The default is to KeepAll if the readwrite file is set up for an intralink restart and Clean otherwise.
IOp Setting Keywords
IOp1=keyword
This keyword controls various details of the operating system interface. The options are standard, but not all are implemented (or even relevant!) in every version.
IOp2
This option sets the maximum amount of memory which will be dynamically allocated. MDV and Core are synonyms for IOp2.
IOp33
This sets the standard debug print option as specified.For example, the following sets IOp(33) to 3 in all invocations of overlay 2, and IOp(33) to 1 in all invocations of overlay 7:
IOp33(2=3,7=1)
The Gaussian 16 IOps Reference also documents all internal options (IOps).
Additional Options to Standard Keywords
CPHF
The following options are used for debugging:
Keep all EE centers in CPHF, even for Opt=CalcFC or Opt=CalcAll with nonquadratic microiterations, where atoms that are not used in internal coordinates need not be included in the CPHF.  
Do not reuse the electric field CPHF solution in the 2^{nd} (nuclear) CPHF during frequency calculations. The default is ReUse.  
Treat real and imaginary perturbations together. The opposite is NoXY, which does them separately. The default is to treat them separately if nuclear perturbations are also being done, but to treat them together if there are only electromagnetic perturbations.  
Use the ZVector method [Diercksen81, Diercksen81a, Handy84] for postSCF gradients. Allowed and the default if HartreeFock 2nd derivatives are not also requested. The NoZVector keyword says to use the full 3 × N_{Atoms} CPHF for postSCF gradients. 
FMM
The following options are available for debugging:
Integral
The following options are used for debugging:
Do calculation in main code using CNDO/2 integrals.  
Do calculation in main code using INDO/2 integrals.  
Do calculation in main code using ZIndo/1 integrals.  
Do calculation in main code using ZIndo/S integrals.  
Use the PRISM algorithm [Gill94] for spdf integral derivatives. This is the default.  
Evaluate oneelectron integrals using the Rys method [Dupuis76, King76, Rys83], instead of the default method. This is necessary on machines with very limited memory.  
If writing twoelectron integrals, use Rys method (L314) [Dupuis76, King76, Rys83, Schlegel84]. This is slower than the default method, but may be needed for small memory machines and is chosen by default if regular (nonRaffenetti) integrals are requested (by the NoRaff option).  
Use scalar Rys integral derivative code. Can combine with Berny for df only using Rys.  
Use Berny sp integral derivative and second derivative code (L702).  
Pass specifies that the integrals be stored in memory via disk, and 

Forbid use of special Coulomb code.  
Do not use the special sp integral program (L311) when writing integrals to disk.  
Reverse choice of diagonal sampling in Prism.  
Do not use Schwartz integral estimates (only use the heuristic set). Schwartz says to use the Schwartz integral estimates in addition to the heuristic set. The default is to use both.  
Reverse choice of Scat20 vs. replicated Fock matrices.  
Turn off extra DFT cutoffs.  
Split AO S=P shells into separate S and P shells. NoSplitSP is the default.  
Split AO S=P=D and S=P=D=F shells into S=P, D, and F. NoSplitSPDF is the default.  
Split density S=P=D and S=P=D=F into S=P, D, and F. NoSplitDBFSPDF is the default.  
Forbid use of gather/scatter digestion, even when processing small numbers of density matrices. Splatter is a synonym for this option.  
Do nuclearelectron Coulomb with electronelectron.  
Do J and K in HF/hybrid DFT separately for testing.  
Set up for parallel 2 electron integral evaluation but then do not run in parallel (for debugging).  
Set up for parallel 2 electron integral evaluation but then do not run in parallel (for debugging).  
Cause Linda workers to run sequentially. Currently just makes the Linda workers other than the master run simultaneously but before the master.  
Make all atom sizes large in XC quadrature.  
Make all shell sizes large in XC quadrature.  
Do not use (Abelian) symmetry to reduce grid points on symmetryunique atoms.  
Convert to linear storage in FoFCou for testing.  
Reverse choice of whether to precompute distance matrix during numerical quadrature. The default is to precompute for molecules but not for PBC.  
Turn off dynamic work allocation. 
Sparse
The following options are used for debugging:
Changing Link Invocation and Ordering
ExtraLinks
This requests that additional links be executed. They are added to all instances of their overlay after the regular links. For example, ExtraLinks=L9997 will cause each instance of overlay 99 to include links 9999 (by default) and 9997, in that order.
ExtraOverlays
This command requests that extra overlay cards be read in nonstandard route format and inserted into the standard route immediately before the final (overlay 99) card.
Skip
Skip initial overlay cards in the route. Skip=OvNNN skip until first occurrence of overlay NNN. Skip=M skip first M cards.
Use=Lnnn
This specifies alternate routes through the program. The following options are available:
Use L123 instead of L115 for IRC. This is the default for IRC, except for IRCMax jobs.  
Use old link 402 code for semiempirical.  
Use link 503 for SCF.  
Use link 506 for ROHF. 
The Standard Orientation in Gaussian
Before a calculation is performed, a molecule can be reoriented to a different coordinate system, called the standard orientation, with the use of molecular symmetry. In geometry optimizations, reorientation occurs at every step; the program then checks if the standard orientation of a molecule has flipped by 180 degrees during an optimization and avoids the flip. This avoids jumps when animating optimizations, IRCs, etc. in GaussView and improves SCF convergence.
This section describes the goals, factors to consider, and various rules for positioning axes for the standard orientation of molecules.
Selection Goals
The goals for selecting conventions for standard orientation are:
 To simplify the 3×3 transformation matrices by reorienting the molecule.
 Two Zmatrices differing in values of internal coordinates but identical in integer quantities (such as occurs on subsequent points of a geometry optimization) should produce the same standard orientation.
 Two different Zmatrices for the same molecule should produce the same coordinates, except for a possible renumbering of atoms.
 Maximizing the number of molecular orbital coefficients which are zero by symmetry.
General Considerations
The factors that should be considered for standard orientation are:
 A righthanded coordinate system is used throughout the calculation.
 The molecule is translated so that its center of charge is at the origin.
 Atoms are not reordered relative to their order upon input.
 The Cartesian axes are considered to increase in priority in the order X < Y < Z.
Rules for Positioning an Axis
Criteria for rotating and aligning an axis are listed below. If rotation is required to meet one of these criteria, it should be a 180 degree rotation about the X, Y, or Z axis, defined as follows:
X  Rotate about Y  
Y  Rotate about Z  
Z  Rotate about X 
An axis of rotation or a principal axis of charge can be aligned with a Cartesian axis in one of two ways—either parallel or antiparallel, depending on the successive application of the following tests until a definite result is achieved:
 The sum of the coordinates of the atoms of the highest atomic number on the axis must be positive.
 The third moment of charge must be positive.
 The sum of the projections of the atomic coordinates onto the reference axis must be positive.
 The first atom with a nonzero projection on the reference axis must have a positive projection on that axis.
Rules for Positioning Principal Axes of Charge
In the absence of any other rules, the principal axis corresponding to the largest principal moment of charge must be aligned with the highest priority Cartesian axis available. Individual point groups have specific considerations:
C_{s}  The molecular plane must be made coincident with the XY plane. Note that although this convention conflicts with Mulliken's suggestion, it is consistent with the character tables of Cotton and Herzberg. The molecule is then rotated about the Z axis according to the rules given below for C_{n} molecules.  
C_{2v}  The molecular plane is placed in the YZ plane, following Mulliken’s recommendation for planar C_{2v} molecules. The following tests are successively applied for nonplanar molecules: (1) The mirror plane with the most atoms is put in the YZ plane; (2) The mirror plane with the most nonhydrogen atoms is put in the YZ plane; (3) The mirror plane with the lowest numbered atom is made coincident with YZ. Finally, the axes of charge rules are applied (as described above).  
Planar, D_{2h}  Following Mulliken's recommendation, the molecular plane is placed in the YZ plane. The molecule is rotated about the X axis so that the Z axis can pass through either the greater number of atoms, or, if this is not decisive, the greater number of bonds.  
C_{n}  Follow the rules for general symmetric top molecules.  
C_{i}  Translate but do not reorient.  
C_{1}  Translate but do not reorient. 
Special Rules for Symmetric Top Molecules
Symmetric top molecules are distinguished by having two of three moments of inertia equal. The third moment can thus be uniquely identified as the reference axis and the point group is analyzed by considering circular sets of atoms.
The following rules are applied for symmetric top molecules:
 The unique axis is aligned with the Z axis.
 A circularset of atoms is composed of atoms lying in a plane which have the same atomic number, and are equidistant from a reference axis perpendicular to the plane. Atoms on the reference axis are not included in any circularset. A circularset of atoms is generated by a proper rotation axis.
 The key atom in a symmetric top molecule is the atom with the lowest number in the key circularset. The following tests are carried out successively to find the key circularset:
 Which set is nearest the XY plane?
 Which set has a positive projection on the Z axis?
 Which set is nearest the Z axis?
 Which set is comprised of atoms with the lowest atomic number?

The orientation is then chosen for the specific point group:
 C_{n}, C_{nh}, S_{n}: The molecule is rotated about the Z axis to maximize the number of pairs of heavy atoms parallel to the Y axis. If no such arrangement is satisfactory, then the key atom is placed in the YZ plane to give it a positive Y coordinate.
 D_{n}, D_{nh}: One of the C_{2} axes is made coincident with the Y Cartesian axis. The tests described below are used to decide which C_{2} axis is so positioned.
 D_{nd}, C_{nv}: One of the vertical planes is made coincident with the YZ Cartesian plane. The tests below are used to decide which plane is so positioned.
 The following are tests for selecting among axes for the D_{n}, D_{nh}, D_{nd}, and C_{nv} molecules:
 Maximize the projection of the key atom on the Y axis.
 If two orientations give the maximum projection on the Y axis, select one with the maximum projection on the X axis.
 For molecules contained in the XY plane, the standard axis orientation rules (see above) are applied to the X axis to complete the orientation specification.
Special Rules for Spherical Top Molecules
Spherical top molecules are distinguished by having their equal moments of inertia and can be characterized by identifying spherical sets of atoms.
A sphericalset of atoms is composed of atoms which are equidistant from the origin and have the same atomic number. Sphericalsets should be ordered in terms of increasing distance from the origin and of increasing atomic number at any one distance. The key atom is the lowest numbered atom in the first sphericalset.
Although not generally the case, it is possible, with appropriate geometric constraints, to have D_{2d}, D_{2h}, or D_{2} molecules that are symmetric tops. Such molecules have three perpendicular twofold axes that are aligned with the X, Y, and Z axes in accordance with the rules given above.
Specifying NonStandard Routes
If a combination of options or links is required which is drastically different than a standard route, then a complete sequence of overlays and links with associated options can be read in. The jobtype input section begins with the line:
# NonStd
This is followed by one line for each desired overlay, in execution order, giving the overlay number, a slash, the desired options, another slash, the list of links to be executed, and finally a semicolon:
Ov/Opt=val,Opt=val,…/Link,Link,…;
For example:
7/5=3,7=4/2,3,16;
specifies a run through the links 702, 703, and 716 (in this order), with option 5 set equal to 3 and option 7 equal to 4 in each of the links. If all options have their default value, the line would be
7//2,3,16;
A further feature of the route specification is the jump number. This is given in parentheses at the end of the link list, just before the semicolon. It indicates which overlay line is executed after completion of the current overlay. If it is omitted, the default value is +0, indicating that the program will proceed to the next line in the list (skipping no lines). If the jump number is set to 4, on the other hand, as in
7//2,3,16(4);
then execution will continue with the overlay specified four route lines back (not counting the current line).
This feature permits loops to be built into the route and is useful for optimization runs. An argument to the program chaining routine can override the jump. This is used during geometry optimizations to loop over a sequence of overlay lines until the optimization has been completed, at which point the line following the end of the loop is executed.
Note that nonstandard routes are not generally created from scratch but rather are built by printing out and modifying the sequence produced by the standard route most similar to that desired. This can be accomplished most easily with the testrt utility.
A Simple Route Example. The standard route:
# RHF/STO3G
causes the following nonstandard route to be generated:
1/38=1/1; 2/12=2,17=6,18=5,40=1/2; 3/6=3,11=1,16=1,25=1,30=1,116=1/1,2,3; 4//1; 5/5=2,38=5/2; 6/7=2,8=2,9=2,10=2,28=1/1; 99/5=1,9=1/99;
The resulting sequence of programs is illustrated below:
A Simple Route Sequence
The basic sequence of program execution is identical to that found in any ab initio program, except that Link 1 (reading and interpreting the route section) precedes the actual calculation, and that Link 9999 (writing to the checkpoint file) follows it. Similarly, an MP4 single point has integral transformation (links 801 and 804) and the MP calculation (link 913) inserted before the population analysis (Link 601) and Link 9999. Link 9999 automatically terminates the job step when it completes.
A Route Involving Loops. The standard route:
# RHF/STO3G Opt
produces the following onstandard route:
1  1/18=20,19=15,38=1/1,3; 
2  2/9=110,12=2,17=6,18=5,40=1/2 
3  3/6=3,11=1,16=1,25=1,30=1,71=1,116=1/1,2,3; 
4  4//1; 
5  5/5=2,38=5/2; 
6  6/7=2,8=2,9=2,10=2,28=1/1; 
7  7//1,2,3,16; 
8  1/18=20,19=15/3(2); 
9  2/9=110/2; 
10  99//99; 
11  2/9=110/2; 
12  3/6=3,11=1,16=1,25=1,30=1,71=1,116=1/1,2,3; 
13  4/5=5,16=3/1; 
14  5/5=2,38=5/2; 
15  7//1,2,3,16; 
16  1/18=20,19=15/3(5); 
17  2/9=110/2; 
18  6/7=2,8=2,9=2,10=2,19=2,28=1/1; 
19  99/9=1/99; 
The resulting sequence of program execution is illustrated below:
A Route Involving Loops
Several considerations complicate this route:
 The first point of the optimization must be handled separately from later steps, since several actions must be performed only once. These include reading the initial molecule specification and generating the initial orbitals.
 There must be a loop over geometries, with the optimization program (in this case the Berny optimizer, Link 103) deciding whether another geometry was required or the structure has been optimized.
 If a converged geometry is supplied, the program should calculate the gradients once, recognize that the structure is optimized, and quit.
 Population analysis and orbital printing are done by default only at the first and last points, not at the relatively uninteresting intermediate geometries.
The first point has been dealt with by having two basic sequences of integrals, guess, SCF, and integral derivatives in the route. The first sequence includes Link 101 (to read the initial geometry), Link 103 (which does its own initialization), and has options set to tell Link 401 to generate an initial guess. The second sequence uses geometries produced in Link 103 in the course of the optimization, and has options set to tell Link 401 to retrieve the wavefunction from the previous geometry as the initial guess for the next.
The forward jump on the eighth line has the effect that if Link 103 exits normally (without taking any special action), the following lines (invoking Links 202 and 9999) are skipped. Normally, in this second invocation of Link 103, the initial gradient will be examined and a new structure chosen. The next link to be executed will be Link 202, which processes the new geometry, followed by the rest of the second energy+gradient sequence, which constitutes the main optimization loop. If the second invocation of Link 103 finds that the geometry is converged, it exits with a flag which suppresses the jump, causing Links 202, 601 and 9999 to be invoked by the following lines and the job to complete.
Lines 1116 form the main optimization loop. This evaluates the integrals, wavefunction, and gradient for the second and subsequent points in the optimization. It concludes with Link 103. If the geometry is still not converged, Link 103 chooses a new geometry and exits normally, causing the backward jump on line 16 to be executed, and the next line processed to be line 11, beginning a new cycle. If Link 103 finds that the geometry has converged, it exits and suppresses the jump, causing the concluding lines (1719) to be processed.
The final instance of Link 601 prints the final multipole moments as well as the orbitals and population analysis if so requested. Finally, Link 9999 generates the archive entry and terminates the job step.
MP and CI optimizations have the transformation and correlation overlays (8 and 9) and the postSCF gradient overlays (11 and 10, in that order) inserted before overlay 7. The same twophase route structure is used for numerical differentiation to produce frequencies or polarizabilities.
The route for Opt=Restart is basically just the main loop from the original optimization, with the special lines for the first step omitted. The second invocation of Link 103 is kept and does the actual restarting.
ReadWrite File Numbers
The following is a list of readwrite files. Those that are permanently on the checkpoint file are marked with the letter P, and those that are temporarily on the checkpoint file are marked with the letter T. T files are saved for use in restarting an optimization or numerical frequency run, but are deleted when the job step completes successfully.
Type  RWF  Description 
P  501  Gen array. 
P  502  /LABEL/—Title and atomic orbital labels. 
503  Connectivity information (MxBond,0),NBond(NAtoms),IBond(MxBond,NAtoms),RBond(MxBond,NAtoms), where arrays are rounded to a multiple of IntPWP.  
504  Dipole derivative matrices (NTT,3,NAt3).  
P  505  Array of copies of /Gen/ from potential surface scan. 
P  506  Saved basis set information before massage, uncontraction, etc. 
P  507  ZMAT/ and /ZSUBST/. 
P  508  /IBF/ Integral Bugger Format. 
509  Incomplete integral buffer.  
T  510  /FPINFO/ FletcherPowell optimization program data. 
P  511  /GRDNT/ energy, First and second derivatives over variables, NVAR. 
P  512  Pseudopotential information. 
P  513  /DIBF/ integral derivative buffer format. 
514  Overlap matrix, optionally followed by absolute overlap and absolute overlap over primitives.  
515  CoreHamiltonian. There are four matrices here: H(α), the α core Hamiltonian; H(β), the β core Hamiltonian; G'(α), the α G' contribution to Fock matrix; G'(β), the β G' contribution to Fock matrix. H(α) and H(β) differ only if Fermi contact integrals have been added. The G' matrices are for perturbations which are really quadratic in the density (and hence have a factor of 1/2 in their contribution to the energy as compared to the true oneelectron terms) but which are computed externally to the SCF.  
516  Kinetic energy and modifications to the α and β core Hamiltonian. These include ECP terms, DouglasKrollHess corrections, multipole perturbations and Fermi contact perturbations. The latter are used for calculations in which the nuclear and electronic Coulomb terms are computed together, such as the Harris functional and PBC calculations. For semiempirical, holds the core Hamiltonian without nuclear attraction terms for use in the initial guess.  
517  Fermi contact integrals.  
518  Multipole integrals, in the order X,Y,Z,XX,YY,ZZ,XY,XZ,YZ,XXX,YYY,ZZZ,XYY,XXY,XXZ,XZZ,YZZ,YYZ,XYZ,XXXX,YYYY,ZZZZ, XXXY,XXXZ,YYYX,YYYZ,ZZZX,ZZZY,XXYY,XXZZ,YYZZ,XXYZ,YYXZ,ZZXY.  
T  519  Common /OptEn/—optimization control for link 109. 
T  520  Electronic state: count and packed string (1+9 integers). 
P  521  Electronic state: count and packed string (1+9 integers). 
P  522  Eigenvalues, alpha and if necessary, beta. 
523  Symmetry assignments.  
P  524  MO coefficients, real alpha. 
P  525  (no longer used) 
P  526  MO coefficients, real beta. 
P  527  (no longer used) 
T  528  SCF density matrix, real alpha. 
T  529  (no longer used) 
T  530  SCF density matrix, real beta. 
T  531  (no longer used) 
T  532  SCF density matrix, real total. 
T  533  (no longer used) 
T  534  SCF density matrix, real spin. 
535  (no longer used)  
536  Fock matrix, real alpha.  
537  Fock matrix, imaginary alpha.  
538  Fock matrix, real beta.  
539  Fock matrix, imaginary beta.  
540  Molecular alphabeta overlap (U), real.  
541  Molecular alphabeta overlap (U), imaginary.  
T  542  Pseudopotential information. 
T  543  Pseudopotential information. 
T  544  Pseudopotential information. 
P  545  /ORB/ – window information. 
546  Bucket entry points.  
547  Eigenvalues (double precision with window: always alpha and beta, even in RHF case).  
P  548  MO coefficients (double precision with window, alpha and if necessary beta). Complex if necessary. 
549  Molecular orbital alphabeta overlap, double precision with window.  
T  550  Potential surface scan common block. 
T  551  Symmetry operaiton info (permutations, transformation matrices, etc.) 
P  552  Character strings containing the stoichiometric formula and framework group designation. 
T  553  Temporary storage of common/gen/ during FP optimizations. 
T  554  Alternate starting MO coefficients, from L918 to L503, real alpha. Also MO coefficients in S^{1/2} basis for L509 and rotation angles from L914 to L508. 
555  Alternate starting MO coefficients, from L918 to L503, imaginary alpha.  
T  556  Alternate starting MO coefficients, from L918 to L503, real beta. Also MO coefficients in S^{1/2} basis for L509 and rotation angles from L914 to L508. 
557  Alternate starting MO coefficients, from L918 to L503, imaginary beta.  
558  Saved HF 2nd derivative information for G1, G2, etc.  
559  Common /MAP/.  
560  CoreHamiltonian (a. o. basis) with 2 j – k part of deleted orbitals added in. (i.e. frozen core).  
P  561  External point charges or SCIPCM informations. 
P  562  Symmetry operations and character table in full point group. 
T  563  Integer symmetry assignments (α). 
T  564  Integer symmetry assignments (β). 
T  565  Lists of symmetry equivqlent shells and basis functions. 
T  566  Unused in G16. 
T  567  GVB pair information (currently dimensioned for 100 paired orbitals). 
P  568  Saved hamiltonian information from L504 and L506. 
P  569  Saved readin window. 
P  570  Saved amplitudes (IAS1,IAS2,IAD1,IAD2,IAD3; only IAS1 and IAD2 for closedshell). 
571  Energy weighted density matrix.  
572  Dipolevelocity integrals <PhiDelPhi'>, X, Y, and Z, followed by R × Del integrals (R × X, R × Y, R × Z).  
573  More SCIPCM information.  
T  574  /MSINFO/ MurtaughSargent program data. 
T  575  /OPTGRD/ Gradient optimization program data for L103, L115, and L509. 
T  576  /TESTS/ Control constants in L105. 
T  577  Symmetry adapted basis function data. 
T  578  A logical vector indicating which MO's are occupied. 
T  579  NEQATM (NATOMS*NOP2) for symmetry. 
T  580  NEQBAS (NBASIS*NOP2+NBas6D*NOp2) for symmetry. 
T  581  NSABF (NBASIS*NOP2) for symmetry. Followed by matching integer character table, always (8,8). 
T  582  MAPROT (3*NBASIS) for symmetry. 
T  583  MAPPER (NATOMS) for symmetry. 
P  584  FXYZ (3*NATOMS) cartesian forces. During PSCF gradient runs, there will be two arrays here: first the PSCF gradient, then the HF only component (needed for PSCF with HF 2nd deriv). 
P  585  FFXYZ (NAT3TT) cartesian force constants (lower triangle). 
T  586  Info for L106, L110, and L111. 
T  587  L107 (LST) data. 
588  Sx over cartesians in the ao basis.  
589  Hx over cartesians in the ao basis.  
590  F(x) over cartesians in the ao basis (all α, followed by all β for UHF) (without CPHF terms).  
591  U1(A,I) — MO coefficient derivatives with respect to electric field and nuclear coordinates.  
592  Electric field and nuclear P1 (AO basis).  
593  Electric field and nuclear W1 (AO basis).  
594  Electric field and nuclear S1 (MO basis).  
595  Magnetic field U1(A,I) — Del(X,Y,Z) then R × (X,Y,Z), 6 α followed by 6 β.  
596  Full MO Fock derivatives in the MO basis, including CPHF terms.  
P  597  Configuration changes for Guess=Alter. 
598  User Name.  
599  Density basis set info: NDBFn, NVar, U0, DenBfn(4,NDBfn), ITypDB(NDBfn), Var(NVar), IJAnDB(NDBfn), IVar(4,NDBfn).  
600  Saved data for intralink restart.  
P  601  Saved structures, and possibly forces and force constants along reaction path. All structures, then all forces, then all force constants. 
602  PostSCF twoparticle density matrix.  
P  603  Density Matrices at various levels of theory. 
T  604  common /drt1/ from drt program … misc integer ci stuff, followed by variable dimension drt arrays. 
P  605  Atomic charges from Mulliken Populations, ESP fits, etc. Bitmap followed by 0 or more NAtoms arrays. Bits 0/1/2/3/4 Mulliken/ESPfit/Bader/NPA/APT. 
606  SCF orbital symmetries in Abelian point group. Alpha and, if necessary, beta, full set followed by windowed set.  
607  Window'd orbital symmetries like rw 606 (always alpha and beta).  
608  IBF for sorted integrals (normally on SAO unit).  
609  Bit map for sorted integrals (normally on SAO unit).  
610  Sorted AO integrals (normally on SAO unit).  
611  NTT maps for sorted integrals (normally on SAO unit).  
612  Some 1E generators for direct CI matrix element generation.  
613  Some more 1E generators for direct CI matrix element generation.  
614  Configuration information for CASMP2.  
615616  Used for CASMP2.  
617  Spinorbit integrals.  
P  618  Nuclear coordinate third derivatives. 
P  619  Electric field derivatives: 1 WP word bit map, dipole, dipole derivative, polarizability, dipole 2nd derivatives, polarizability derivatives, hyperpolarizability. 
620  Magnetic field derivatives for GIAOs.  
621  Susceptiblity and chemical shift tensors.  
622  Partial overlap derivatives (<MudNu/da>, NBasis*NBasis*NAt3).  
P  623  BornOppenheimer wavefunction derivatives (<Phid2Phi/dadb> for electronic Phi and a,b nuclear, NAt3TT). 
624  Unused in G16.  
625  Expansion vectors and AY products from CPHF, in the order Y α, AY α, Y β, AY β.  
626  MCSCF MO 1PDM (NTT).  
627  MCSCF MO Lagrangian (NTT).  
628  MCSCF MO 2PDM (NTT,NTT) or NVTTTT.  
629  AO 2PDM (shell order).  
T  630  MCSCF information. 
631  PostSCF Lagrangian (TA, then TB if UHF).  
632  O*V*3*NAtoms, followed by O*V*NVar d2E/d(V,O)d(XYZ,Atom).  
P  633  Excitedstate CI densities. 
T  634  SCF Restart information (alpha, then possibly beta MOs). 
P  635  CIS and CASSCF CI coefficients and restart information. 
636  NBO analysis information.  
637  Natural orbitals generated by link 601.  
640  MCSCF data or CIS AO Tx's for 2nd derivatives.  
641  MCSCF data for 2nd derivatives.  
642  MCSCF data for 2nd derivatives.  
643  MCSCF data for 2nd derivatives.  
644  MCSCF data for 2nd derivatives.  
645  MCSCF data for 2nd derivatives.  
646  MCSCF data for 2nd derivatives.  
647  MCSCF data for 2nd derivatives.  
648  MCSCF data for 2nd derivatives.  
649  Eigenvalue derivatives (noncanonical form even if done canonically).  
650  2PDM derivatives, (LenTQ,NDeriv,ShellQuartet) order.  
651  Full U's, canonical or noncanonical as requested.  
652  Generalized density derivatives for the current method (NTT,NDeriv,IOpCl+1).  
653  Lagrangian derivatives for the current method (NTT,NDeriv,IOpCl+1).  
654  Gx(Gamma).  
655  G(Gamma).  
656  Nonsymmetric S1 and S2 parts of Lagrangian for MP2 or CIS second derivatives.  
657  t*Ix and t*Ix/D matrices from L811 for L1112.  
658  L(x) from L1111.  
659  MO correlated W for correlated frequencies.  
660  2nd order CPHF results: Pia,xy, Sxy, Fxy (complete) all in MO basis, PSF α then PSF β if UHF.  
661  Computed electric field from L602.  
662  Points for electrostatic evaluation.  
T  663  Saved information for L117 and L124. 
664  Spin projection data.  
P  665  Redundant coordinate information. 
666  (no longer used)  
667  CIS AO Fock matrix.  
668  CIS Gx(T) matrices.  
669  Saved /ZMat/ and /ZSubst/ during redundant optimzations.  
P  670  New format basis set data (compressed /B/). 
P  671  New optimization (L103/L104) data. 
P  672  Unused in G16. 
673  Global optimization data.  
674  ONIOM internal data.  
675  Saved files for LS during ONIOM.  
676  Saved files for MS during ONIOM.  
677  Saved files for LM during ONIOM.  
678  Saved files for HS during ONIOM.  
679  Saved files for MM during ONIOM.  
680  Saved files for LL during ONIOM.  
681  Saved files for HM during ONIOM.  
682  Saved files for ML during ONIOM.  
683  Saved files for HL during ONIOM.  
684  SABF information for DBFS: equivalent to files 577 and 581 for AOs.  
685  Cholesky U, or transformation to surviving basis functions.  
686  Cholesky U^{1}.  
687  Molecular mechanics parameters.  
688  Density in orthogonal basis (α spin) for ADMP or sparse SCF.  
691  Saved initial files during ONIOM (gridpoint 17, hence 674+17=691).  
694  Permutation applied to MOs for postSCF symmetry.  
695  Magnetic properties.  
696  Saved magnetic field density derivatives.  
698  Saved initial structure during geometry optimization, in standard orientation, also used for constraints with the force constants following the structure.  
699  Density in orthogonal basis (β spin) for ADMP or sparse SCF.  
700  Saved /Mol/ for ONIOM.  
701  Saved Trajectory/IRC/Optimization history.  
702  Fit density for Coulomb.  
703  Fit density for Coulomb.  
704  Saved XC contribution to electric field F(xa) for polar derivatives.  
P  710  Basic PCM information. 
P  711  Other PCM data. 
P  712  Non equilibrium data for PCM. 
713  Saved information for RFO with ONIOM microiterations.  
714  Saved model system information for ONIOM microiterations.  
715  Saved rigid fragment information for ONIOM microiterations.  
T  716  Saved copy of basis set data for counterpoise. 
T  717  Saved copy of ECP data for counterpoise. 
T  718  Saved copy of fitting basis for counterpoise. 
719  Saved DiNa information.  
P  720  Saved DiNa information. 
721  Frequencydependent properties.  
722  Derivatives of frequencydependent properties.  
723  Density fitting matrices (metrics).  
724  Density fitting basis (same format as /B/).  
725  DBF symmetry information (NEqDBF(NDBF,NOp2),NEqDB6(NDBF6D,NOp2)).  
726  DBF shell symmetry information (NEqDBS(NDBShl,NOpAll)).  
727  F(x)(PPfit) for density fitting second derivatives.  
728  PBC cell replication information.  
729  Alternate new guess during optimizations.  
730  Counterpoise input specification.  
731  Counterpoise intermediate data.  
732  Basis set for finite nuclei.  
733  PBC Cell scalars and integer cell indices.  
734  Statespecific input parameters for SACCI.  
735  Excitation lables of SAC and SACCI.  
736  Eigenvalues and eigenvectors of SAC and SACCI.  
737  H matrices and their indices of nonzero elements used for SAC/SACCI.  
738  Saved atomic parameters for DFTB/EHTSC.  
739  Temporary storage for imaginary core Hamiltonian perturbations.  
740  Orbital information for SAC/SACCI gradients and PES by GSUM.  
741  MOD Orbital information for SAC gradients.  
742  Saved quadrature grid.  
743  Alpha Fock matrices in orthonormal basis for ADMP, also alpha HF Fock matrix for nonHF postSCF.  
744  Beta Fock matrices in orthonormal basis for ADMP, also beta HF Fock matrix for nonHF postSCF.  
745  Kintegration mesh information.  
746  Eigenvalues and orbitals at all kpoints.  
747  Information for external lowlevel calculations for ONIOM.  
748  TS vector information for ONIOM TS optimizations.  
749  Conical intersection information for ONIOM.  
750  Not used in G16.  
751  Temporary storage for SO ECP integrals.  
752  Pseudocanonical MO Fock matrix for ROMP and ROCC.  
753  Data for FD polar derivatives.  
754  Saved PCM charge derivatives.  
755  PCM inverse matrices.  
756  Charge information for ONIOM.  
757  MO:MO embedding charge data for L924.  
758  Derivatives of embedding charges, when computed explicitly.  
759  Basis set info for density embedding.  
P  760  Full set of pseudocanonical orbitals for RO. 
761  Charges from external PCM iterations (both L117 and L124).  
762  Saved weights for nonsymmetric Mulliken analysis.  
763  File for FC/HT integrals.  
764  File for FC/HT integrals.  
P  765  Saved normal modes. 
766  Saved QuadMac vectors (temporary).  
767  CIS coefficients reordered by symmetry.  
768  Semiempirical parameters.  
769  Saved MOs during numerical differentiation.  
P  770  Saved groundtoexcited state energies and transition moments. 
771  EOM iteration information.  
772  Symmetry operations and character table in Abelian point group.  
989  Multistep job information (1000 reals and 2000 integers).  
990  KJob info in some implementations.  
991  Holds file names, ID's and save flags.  
992  Used for link substitution information in some implementations.  
993  COMMON /INFO/  
994  COMMON /PHYCON/  
995  COMMON /MUNIT/  
996  COMMON /IOP/  
P  997  COMMON /MOL/ 
P  998  COMMON /ILSW/ 
999  Overlay data. 
Last updated on: 05 January 2017. [G16 Rev. C.01]