Subject: Re: CCL:DFT & metal metal bonds

From: Marcel Swart <[email-masked]>
Date: Thu, 20 Jul 2000 08:50:20 +0200

>Sorry,
>
>for wasting bandwidth, but in my last post to CCL. I forgot to mention,
>that if the metal-metal bond distance was fixed to the experimentally
>observed shorter distance, the energy was found to be ca. 5 kcal/mol
>higher than the geometry optimized structure with the longer M-M
>distance. Also, I forgot to mention that I tried polarisation functions
>as well (also numerical basis sets i.e. Dmol). I have not tried STO's
>yet. Perhaps I should give ADF a try?

The answer is a definite YES.

Furthermore, did you also include relativistic effects ?
I guess when you look at Tungsten/Molybdenum, these can be quite significant.
Again this is a YES to ADF, since in this program these effects are 
easily taken into account.

Marcel.

---

From: Marcel Swart <[email-masked]>
Date: Thu, 20 Jul 2000 10:21:48 +0200

>You want to elaborate on this? Is it because of the STOs? As to GTO's I
>use TZVP/P basis sets, which are not too bad usually.

Yes, the STO's are always much better. But not only that. It is a 
very clever program, making the calculations very efficient when 
looking at CPU-time, parallellization, those kind of things.

>yes, scalar relativistic via the ECP.

Well, that's not really what I meant. You assume that the ECP's mimic 
the relativistic effects you are after, but it is not the same as 
including the relativistic effects themselves !!!

>  > easily taken into account.

Also, I know from work from my Professor (yet unpublished I think), 
who is an expert in Relativistic Quantum Chemistry (J.G. Snijders), 
that these relativistic effects are needed for heavy atom dimers. If 
you don't include them (properly), the calculations are not 
performing very well.

Marcel.