Subject: QMC

From: Michael Towler <[email-masked]>
Date: Tue, 29 Feb 2000 21:33:07 +0000 (GMT)

Dear all,

Quantum chemistry problem from a physics lab:

I/we are looking for a package to generate ground and excited state wave
functions for molecules to be used as trial wave functions in our quantum
Monte Carlo code (extending our previous work on solids). Such a package
needs to have the the following capabilities: 

(1) HF/DFT/CIS (CIS being the tricky but essential one to find).

(2) Freeform input pseudopotentials. We have very specific pseudos
tabulated on a grid for use in our QMC program. These neeed to be expanded
in a basis set of Gaussians times powers of r for use in quantum chemistry
packages. Because we need very accurate expansions, we require as few
restrictions as possible on (a) the range of powers of r and (b) on the
maximum number of basis functions in the expansion. 

(3) It needs to be fast and available for parallel platforms. In the
latter case we have access to a Hitachi SR2201, a 64 CPU (R12000) SGI
Origin 2000 and a Cray T3E. We need to do some very big CIS calculations
which are beyond the reach of workstations.

(4) not outrageously expensive ($$) 

(5) clearly documented output for conversion into format appropriate for
hungry QMC code.

Accessible source code would also be nice, but I guess we can do without
it.

We've been using Gaussian94 to do the above up to now, but it has severe
limitations in the area of general ECPs i.e. acknowledged bugs and/or
array size limitations which prevent us expanding the pseudos sufficiently
accurately.. Gaussian98 appears to have corrected these problems to some
extent but for reasons of either non-existence or lack of money it is not
available on the parallel machines accessible to us. I don't mean any of
the above as a criticism of the otherwise lovely Gaussian package - but
these are genuine problems that I can't see a practical way around at the
moment.

I'll summarize any replies.

Thanks,
Mike

PS: If anyone has a piece of code to perform an expansion of an arbitrary
pseudopotential in a basis of gaussians times powers of r, and is prepared
to share its secrets with me, I'd be interested to compare it with my own
attempt.. ;-) 

-------------------------------------------------------------------------
Dr. Mike Towler ([email-masked]) Theory of Condensed Matter (Rm 524)
  Cavendish Laboratory, University of Cambridge, Cambridge  CB3 0HE, UK
Tel. +44-(0)1223-337459                           Fax. +44-(0)1223-337356
----------------WWW: http://www.tcm.phy.cam.ac.uk/~mdt26/ ---------------