Availability of methods

Questions
#1

Dear Q-Chem team,

the following is not only a Q-Chem issue but is unfortunately true also for other QC programs…

It is quite often the case that methods are not available for all combinations, e.g. solvation or faster ERI-methods, e.g. OCC-RI. This not always documented in the manuals, unfortunately.

I have two annoying recent examples of a multiple core RRAMAN job, which stopped after 48 h with the following messages:

  1. hamiltonian: no capability for term occrik_ds:ohess
  2. hamiltonian: no capability for term scrf_hcore:fock_deriv

I reckon this should tell me that neither the occrik nor the CPCM
method is available for this part of the program.

What I really wonder is, why could the program check this not right away at the start??

1 Like
#2

Q-Chem is a complicated software with a lot of moving parts, and there’s no realistic way to test all possible combination of options a priori. The way that we find out about these things is when users point them out, so if you could post an input file that demonstrates the problem then we can add it to the list of conflicting or unavailable combinations of input options that are checked at the beginning.

In general, when testing a new combinations of options that you’ve never tried before it is a good idea to test a small molecule and small basis set to see that the job runs, rather than starting with a calculation that takes two days.