From owner-chemistry@ccl.net Fri Oct 28 12:51:01 2011
From: "Arne Dieckmann adieckma**googlemail.com" <owner-chemistry{}server.ccl.net>
To: CCL
Subject: CCL: DFT and dispersion
Message-Id: <-45764-111028124925-19206-id/b+IpiyAG83YmFaZ91/A{}server.ccl.net>
X-Original-From: Arne Dieckmann <adieckma ~~ googlemail.com>
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Date: Fri, 28 Oct 2011 09:49:15 -0700
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Sent to CCL by: Arne Dieckmann [adieckma[A]googlemail.com]
First, I would like to thank all of you for your comments and help. I strongly believe in the principle of getting the right answers for the right reasons, which is why I want to make sure I am using methods in the context they were developed for. With regards to solution corrections: As the DFT-D3 model is only geometry-dependent, I guess the following procedure would be valid: 

1. Optimize the geometry in the gas phase 
2. Calculate energy in solution (e.g. using SMD) 
3. Add DFT-D3 dispersion correction 
4. Add thermal corrections 

Would you agree? 


Cheers, 
Arne


On Oct 28, 2011, at 4:16 AM, Stefan Grimme grimme]![thch.uni-bonn.de wrote:

> 
> Sent to CCL by: "Stefan  Grimme" [grimme _ thch.uni-bonn.de]
>> By the way, do you know how well DFT-D3 works with implicit solvation? I guess in this case the >parameters would have to be solvent    -dependent, right?
> 
> One important comment on this point: DFT-D3 (and similarly other dispersion corrections) are constructed to yield accurate isolated molecule (gas phase) energies and geometries. These can be combined with any kind of solvation model and when this model accurately accounts for solvent-solute dispersion,
> everything is consistent. What could be done in principle as suggested (to modify the intramolecular dispersion to implicitly account for solvent-solute dispersion) is theoretically not justified in my opinion.
> DFT-D3 has been developed to reproduce CCSD(T)/CBS as closely as possible and should not be used as an empirical tool to balance inter- and intra-molecular effects. 
> A further note in this context: this balance of intramolecular and intermolecular dispersion is also the reason why in some cases dispersion-UNcorrected DFT seemingly provides better results compared to experimental solution data than physically correct methods. But when one wants to get the right result for the right reason I would prefer to first treat the gas phase system as accurately as possible and then to add the best available condensed phase corrections. And this holds for DFT as well as WFT methods.
> 
> Best wishes
> Stefan Grimme
> grimme],[thch.uni-bonn.de> 
>