Subject: combination of b3lyp and cc-pVQZ

From: Harald Bock <[email-masked]>
Date: Mon, 27 Aug 2001 14:14:08 +0200

Dear reader,
I have a question about combining methods and basis sets:

does it make sense to run a calculation usin eg b3lyp using a cc-pVQZ
basis set. I am interested in opt, freq (raman) and nbo results.

 Harald Born

 Please send answers to
 
 [email-masked]

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From: Marcin Krol <[email-masked]>
Date: Mon, 27 Aug 2001 16:07:45 +0200 (METDST)

Dear CCLers,

Sorry for another hardware question, but as I followed the discusion on
AMD vs Intel processors it occured to me that the former are faster and
cheaper than the latter but the problem was the lack of dual AMD
motherboards. Now Tyan has delivered two dual AMD motherboards (Thunder
and Tiger). As Thunder (S2462) is unfortunately too expensive (for my
budget at least), I thought that a PC with Tyan Tiger (S2460) and 2 AMD MP
processors would be a great computer for MD and QM/MM simulations - fast
and not so expensive. However, I haven't found any benchmarks for dual AMD
computers on any MD code. Does anyone use such a computer for MD and/or QM
calculations? Is it good, or is it better to buy dual PentiumIII system?
Or maybe wait for other dual AMD motherboards (MSI and ASUS are
said to be preparing such motherboards)?

Any comment on dual AMD configuration and/or performance would be
appreciated.

Thank you in advance
Sincerely
Marcin Krol

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From: elewars <[email-masked]>
Date: Mon, 27 Aug 2001 11:54:20 -0400

Hello,

DFT calc's seem to be "saturated" by basis sets more quickly than are ab initio:
Merril et al noted that "Once the double split-valence level [e.g. 6-31G*] is
reached, further improvement in basis set quality offers little in the way of
structural or energetic improvement.' [1]. Stephens et al. report that "B3LYP
calculations converge rapidly with increasing basis set size and that the
cost-to-benefit ratio is optimal at the 6-31G* basis set level. 6-31G* will be
the basis set of choice in B3LYP calculations on much larger molecules [than
C5H6O2]." [2]. We have found (albeit in a limited number of calculations) only
very small differences (up to 4 kJ mol-1) between 6-31G* and 6-311G* basis sets
with the BP86 functional.

But you could do some test calculations using B3LYP/6-31G* and B3LYP/cc-pVQZ.

[1] G. N. Merrill, S. Gronert, S. R. Kass, J Phys Chem A, 1997, 101, 208.
[2] P. J. Stephens, F. J. Devlin, C. F. Chablowski, M. J. Frisch, J Phys Chem
1994, 98, 11623, and refs therein.

E. Lewars
=========

Harald Bock wrote:

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From: "Owen Lewis" <[email-masked]>
Date: Mon, 27 Aug 2001 11:44:23 -0400

Try www.tomshardware.com for benchmarks and performance comments on the two
Tyan motherboards - there may be something there.

I can unfortunately only personally comment on the performance of the
motherboard itself - we have used the Tyan Tiger board with twin PIII 733
chips and the performance is excellent.  I would imagine one would obtain
excellent results using AMD processors.

cheers,

Owen Lewis
Molecular Modelling Product Developer
SimBioSys Inc.
Toronto, Ontario

[email-masked] Original Message -----
From: "Marcin Krol" <[email-masked]>
To: <[email-masked]>
Sent: Monday, August 27, 2001 10:07 AM
Subject: CCL:Dual AMD motherboard