[molpro-user] CCSD convergence criteria & restart

[Matt Hodges]

>>>>> Daniel Svozil writes:

 > I am trying to understand when CCSD is considered to be converged.
 > According to manual
 > (http://www.molpro.net/info/current//doc/manual/node322.html)

 > "The convergence thresholds can be modified using

 > THRESH,ENERGY=thrden,COEFF=thrvar

 > Convergence is reached if the energy change is smaller than thrden
 > (default 1.d-6) and the square sum of the amplitude changes is
 > smaller than thrvar (default (1.d-10)."

 > What are amplitude changes? VAR(S) and VAR(P)? And what those
 > variables actually mean? Change in sibles and pairs energies?

These are the sums of the squares of the amplitude changes between
each pair of iterations [N and (N - 1)] for the singles and pairs,
respectively.

 > There is also global directive GTHRESH, where COEFF key means
 > "Convergence threshold for coefficients in CI and CCSD (default
 > 1.d-4)"
 > (http://www.molpro.net/info/current//doc/manual/node62.html#command:gthresh),
 > but this is apparently different that what is said at CCSD THRESH
 > manual page. And moreover it seems to me, that the implicit value
 > of COEFF is 1.d-5.

 > How to print out CCSD coefficients to the output file?

At present, you can use:

    ccsd
    print,cs=2,cp=2

to increase the print level, and this will output the singles (T1) and
doubles (TIJ) amplitudes (and some other quantities) for each
iteration.

 > I have very slowly converging dipole-bound anion and I would like
 > to relax convergence criteria, the energy change is negligible and
 > constant (1d-8), but the job doesn't stop here.

You can control these thresholds in the way quoted from the manual
above. So, for example:

    ccsd
    thresh,coeff=1d-3,energy=1d-5

will lead to THRVAR = 1.00D-06 and THRDEN = 1.00D-05.

 > Also, is it possible to restart CCSD calculation from the last
 > already done iteration (for both open (rsscd(t)) and closed shell
 > systems)? When I write int and wfu files and I use them in the next
 > run, only HF reference is restarted, but not CCSD.

I don't think this is possible at present.

-- 
Dr. Matt Hodges
School of Chemistry
University of Birmingham