Subject: Re: CCL:Comparative Linux quantum chemistry benchmark

From: "Dr. Peter Burger" <[email-masked]>
Date: Mon, 6 Dec 1999 12:56:16 +0100 (MET)

Dear Marcel,
 
 thanks for your E-mail and comments.
 
 > a benchmark usually means checking DIFFERENT programs on ONE machine, or
 > ONE program on DIFFERENT machines. This makes the benchmark meaningful.
 
 I agree, however, due to license restrictions, life is not always
 that simple in that I could not perform all the benchmarks on an identical
 machine. However, where it was possible, the benchmarks data displayed
 an excellent correlation with the clock frequency (slope of .99) in that
 that seems not to be too much of a concern if at all.
 
 > BTW, are the default grids the same for all programs ? Do they all use
 > numerical integration, and if so, are the energies all the same, up to the
 > same accuracy ? Is the numerical integration valid up to the same accuracy,
 > etc. etc. ?
 
 Energies are hard to compare since different basis sets _have_ to be used
 STO's for ADF, GTOs for most of them and numerical for
 Dmol.. The default grids were not always identical, some of them use
 modified grids, which cannot always be controlled by the
 user.. Essentially, it's better to see this comparison more as an applied
 benchmark for applied chemists using the default settings. Even more 
 matters actually the number of cycles that are required with the same 
 convergence criteria.  This may vary from 10-28 cycles!!! and that the
 programs achieve convergence at all! which is definitely _not_ the case
 for transition metal complexes I am interested in.
 
> > Else, these times do not say anything more, than that you have had a nice
> > time, the afternoon you were playing with these programs.
 
 For me, it's actually more than _playing_ since time for completion
 matters to me. However, obviously there are more points to that including
 the quality of optimizers, SCF-convergence, flexibility of the programs,
 for instance to do an unrestricted/Cosmo/ECP run on open shell
 transition metal systems is not all that simple for a number of programs
 which I had to learn the hard way. So, the message is get the job
 done! For instance the ridft method in Turbomole is so fast in parallel
runs (and still accurate) that you can treat even large systems fully
quantum mechanically and have not resort to hybrid methods.

 Peter
-------------------------------------------------------------
Peter Burger
Anorg.-chem. Institut 
Universitaet Zuerich
[email-masked]