CASINO manual - Theory of Condensed Matter

% mv Test.FChk dna.Fchk
run gaussiantoqmc . . . and follow the prompts
% mv dna.qmc gwfn.data
run casino.
The code should automatically detect what sort of gaussian job it is and give you the opportunity
to construct an excited-state wave function if applicable.
It can deal with the following sorts of calculation:
• HF and DFT ground states, open and closed shell.
• CIS excited states, open and closed shell.
• CASSCF states. Getting gaussian to output these can be problematic for large calculations.
It is possible that gaussiantoqmc will get confused if you use some combination of IOps other
than those described in Sec. 8.6.3.
• Time-dependent HF (TD-HF) or DFT (TD-DFT) excited states.
If the user chooses to output a CIS or TD-DFT wave function, they are given the option of resumming
it. The wave function must also be resummed if the user wishes to analyse its composition. As
distributed, gaussiantoqmc will not do this analysis but if you wish to switch this option on then the
flag analyse cis in cis data.f90 must be set to T and gaussiantoqmc recompiled.
With this flag set the code evaluates the percentage contribution of each single excitation to the CIS
expansion. Degenerate virtual and occupied orbitals are identified and their contributions summed.
The final output takes the form of files called fromi j.dat where i–j indicates a range of degenerate
occupied orbitals (if i = j then i is a nondegenerate orbital). These files detail all excitations out
of the specified orbitals along with a percentage giving their contribution to the CIS expansion as a
whole. The sum of the percentages (final column) from each of the fromi j.dat should be 100 if
everything is working OK.
8.6.2 Other features of GAUSSIANTOQMC
The code also contains some crude normalization and plotting routines that are really just debugging
aids. By setting the flag test=T in gaussiantoqmc.f90 and recompiling, the user is given the option
of plotting and testing the normalization of individual molecular orbitals. The axis along which the
plotting is done is set in wfn construct.f90 and this must be hacked if the user wishes to change
things.
8.6.3 Getting GAUSSIAN to do what you want
In principle, gaussian can do an awful lot of things. In fact, some of these things seem to require
magical incantations. These will be described in this section, broken down into the different calculations
to which they apply. The comments on g98 refer to revision A9 and may depend on which
version is used.
General bits and pieces
Some points to note:
• Both g94 and g98 appear to have formatting errors when printing out the Gaussians used in
the ECP expansion—large exponent values are replaced with stars. This does not affect the
subsequent calculation.
• g94’s ECP (pseudopotential) package will not accept expansions containing more than 13 Gaussians
per angular-momentum channel.
• g98’s ECP integral package crashes when one attempts to do a large (both in terms of basis
and ECP expansion) calculation with symmetry switched on. The solution to this is to switch
symmetry off using ‘Nosymm’.
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