Subject: RE: dft question on sugar

From: "Gabor I. Csonka" <csonka ## web.inc.bme.hu>
Date: Fri, 4 Feb 2005 11:37:32 +0100

Probably you can build on my earlier work too.
In general I can say that we should distinguish between short-range part of
the van der Waals (vdW) interaction and the long range part. The short range
part can be well described with non empirical functionals as PBE or TPSS.
The long range part not, it requires correction.

In general, the strong (and short) H-bonds can be reasonably described with
DFT functionals as B3PW91 or B3LYP provided that a reasonable basis set is
used I suggest 6-31+G(d,p) or 6-311+G(d,p). Reference:
Csonka, G. I. Proper basis set for quantum mechanical studies of potential
energy surfaces of carbohydrates 
J. Mol. Struct. (THEOCHEM),  2002, 584, 1-4.

Lot of other references are summarized in (some of them are preprint):
http://web.inc.bme.hu/~csonka/p96.html

Best regards, Gabor I. Csonka

> -----Original Message-----
> Hi I want to know if there are someone expert in DFT calculation methods
> on
> carbohydrates?
> 
> My question is: which  is or which are the best functionals for dft that
> describe correctly hydrogen bond and weak interaction like van der walls
> etc
> in sugar moieties?
> 
> Now I9m using b3lyp but it under estimate that kind of forces in my
> experiments...while hf overestimate these effects.
> 
>