| Q0. | How can I get the most recent Updates and Bug Fixes? |
| Q1. | Does NBO 5.0 work with Gaussian 03? |
| No. However, NBO 5.G is designed to link with Gaussian 03 and appears to support all non-PBC Gaussian wavefunction options. | |
| Q2. | For some reason the NRT (or STERIC, CMO, FIXDM, NCS, NJC, etc.) keyword isn't accepted, even though I have the latest version of Gaussian. What's wrong? |
| Gaussian program packages such as Gaussian 03 or Gaussian 98 are distributed with NBO 3.1 (the program version of late-1980s vintage). You must upgrade to a more recent NBO version (curently, NBO 5.0 or NBO 5.G) in order to have access to these newer NBO-based analysis options (but see Q3). | |
| Q3. | How can I use NBO 5.0 with G98W or G03W? |
|
The Windows-based binary programs G98W or G03W contain
embedded L607 "NBO 3.1"
that cannot be replaced by NBO 5.0. However, the ARCHIVE files
produced by NBO 3.1 are still readable by all post-1980s versions
of the NBO program,
including GENNBO 5.0W. A practical strategy is therefore to
use G03W/NBO3 to generate ARCHIVE (.47) files, which are subsequently used as
input to GENNBO 5.0W for NRT, STERIC, CMO, PLOT,
and other newer options. [Note, however, that the intrinsically
interactive options (NCS, NJC, NEDA, $DEL) cannot be
performed by stand-alone GENNBO 5.0W.] Details of FILE47
format and general GENNBO program usage are given in the NBO 5.0 manual.
The specific steps are as follows: First, prepare the NBO archive (.47) file from your Gaussian run. To do so, just include the "archive" keyword and chosen filename "file=myjob" in the $NBO keylist of your Gaussian input file (with the usual POP=NBOREAD on the route card). You should find the "myjob.47" file produced by this run. Second, modify the myjob.47 file by adding desired keyword options to the $NBO...$END keylist in the second line of this file. Then, with myjob.47 in the same directory, either (a) run GENNBO 5.0W and follow the prompts, or (b) run your OS-specific GENNBO (created with ENABLE.F and system compilers) from the OS prompt, with myjob.47 as standard input (viz., GENNBO < myjob.47 > myjob.out). |
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| Q4. | With Gaussian I tried to evaluate NPA charges at a correlated MP2 level, but the results seemed to be identical to uncorrelated HF results. What's wrong? |
| You must include "DENSITY=CURRENT" (or "DENSITY=MP2") in the Gaussian route card to analyze higher-level corrections to the HF density. | |
| Q5. | My G98 job didn't produce any NBO output but instead gave the message, "NBO is unable to handle linearly dependant basis sets." What does this mean, and what can I do? |
| G98 checks for numerical instabilities due to near-linear dependence of basis functions (chiefly due to inclusion of diffuse functions) and reduces the dimension of the basis set if necessary. When this occurs, G98 prints the above error message and bypasses entry to NBO. One possible solution is to run the same job with G94 or earlier G9X versions. (This usually works, because NBO has its own checks for numerical instabilities.) Another solution is to include IOP(3/32=2) to bypass the G98 linear dependence test. However, if linear dependence is truly severe, the only alternative may be to remove "+" or other basis functions until the G98 linear dependency fix is not triggered. | |
| Q6. | When I perform $DEL deletions with Gaussian, the program says that the SCF is "not converged." Does this indicate an error? |
| No. The $DEL procedure uses the converged Fock (or Kohn-Sham) operator for single-pass energy evaluation of a deleted density that differs from the "converged" (full) density. Hence, this message can be safely ignored. | |
| Q7. | I compared NPA from a job run on Jaguar and Gaussian and found that many NAO populations differ in the two programs. Who's right? |
| Both are. If internal input coordinates are employed, different program systems often use a different choice of cartesian coordinate system. Under these conditions, the meaning, e.g., of "x" is different (relative to molecular orientation) in the two calculations, and the populations of "p(x)" NAO will differ accordingly. Nevertheless, the two programs should give all the same NAO populations if the coordinate axes are chosen consistently. | |
| Q8. | My MP2 calculation under Gaussian led to many warning messages about "non-physical" occupancies and eventually stopped. What's wrong? |
| MP2 and related methods lead to a perturbative approximation to density that is not physically consistent with an N-particle wavefunction (i.e., not N-representable) order by order. These perturbative inconsistencies are insignificant when the perturbative series is well behaved, but they sometimes become serious (forcing abandonment of NBO analysis) for spin-contaminated open-shell systems and other ill-converged cases. In such cases the NBO error messages warn that the MP2 density is unreliable. The FIXDM keyword can suppress some of these error messages, but cannot "correct" for a physically non-convergent perturbation expansion. | |
| Q9. | My NRT job goes into an infinite hang that requires killing the job. How can I recognize that the job is hung, and what can I do to prevent it? |
| The hang probably results from a case where apparent hypervalency was detected and the program attempted to restart NRT with the NRTFDM option using the full (rather than valence-only) density matrix, but without sufficient memory to accomodate necessary reference structures. (Look for the "apparent hypervalency" message near the bottom of the .LOG file to see if this type of hang is likely.) The solution is to provide LOTS of memory for possible hypervalent cases, and/or to include the NRTFDM keyword so that the full density matrix is used from the outset. In this case, inadequate memory will lead to an early abort, rather than an infinite hang. | |
| Q10. | I tried to go to a higher-level MP2 or CASSCF treatment, but suddenly there were no NBO orbital energies and no table of 2nd-order perturbative energies? What's wrong? |
| NBO evaluates "orbital energies" and 2nd-order stabilization energies only when there is a well-defined 1-electron effective Hamiltonian operator (e.g., Fock or Kohn-Sham operator). Such an operator is unavailable for correlated descriptions, except those of DFT type. | |
| Q11. | I often see a warning message about "population inversion" after NPA analysis. Should I be worried? |
| Probably not. The "inversion" (occupancy ordering inconsistent with energy ordering) probably occurs for Rydberg-type orbitals of very low occupancy or near-degeneracy in occupancy or energy, so that no significant physical effects are indicated. The contrary case of an "inversion" involving high-occupancy, non-degenerate orbitals indicates an excited state. | |
| Q12. | How can I get orbital diagrams of NBOs or other natural localized orbitals? |
| If the ESS has integrated NBO and a read-write file, the checkpointing (or SPARTAN) options may allow you to use standard MO-plotting methods to plot the localized orbitals written (over the MOs) into this file. The NBOView utility program (see order info) provides a more general way to obtain 1-d amplitude profiles, 2-d contour plots, or rendered 3-d photograph-like images for any desired localized orbitals, using the input files created by the PLOT keyword. NBOView orbital imagery is illustrated in the homepage logo and elsewhere throughout this website. | |
| Q13. | I can't compile gennbo.f with the g77 compiler on my linux system. What's wrong? |
|
Use the compiler directive
to bypass checks for strict consistency between defined vs. called subroutine argument lists. |
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| Q14. | My NBO_50.SRC file contains many "^@" control characters that were not on the original CD. What happened? |
| The .SRC textfile may have been transferred between different operating systems using a Windows-type ftp utility with "T/B" (rather than text "T") as the default file-type setting. | |
| Q15. | I am working with lanthanides and/or actinides. Does the NPA partitioning scheme recognize the 5d (for lanthanides) and 6d (for actinides) subshell as a "valence" subshell, and will this affect my NPA charges? |
| The current version of NBO 5.G recognizes these subshells as valence orbitals, consistent with the observed partial occupancy of these subshells in certain ground-state atoms of the "f-block" lanthanides and actinides [J. Comput. Chem. 28: 198-203, 2007]. (The NPA partitioning for lanthanides/actinides is now consistent with long-established treatment of main and transition blocks and known ground-state atomic configurations. Older NBO versions conformed to the Madelung Rule, which forces some lanthanides and actinides to be analyzed in terms of excited-state atomic configurations.) This change can affect the NPA charges [J. Chem. Phys. 121, 2563-2570, 2004]. For the code-change to make older NBO versions consistent with current NBO 5.G in this respect, please see the update. |