From owner-chemistry@ccl.net Fri Oct 28 11:43:01 2011 From: "Stefan Grimme grimme]![thch.uni-bonn.de" To: CCL Subject: CCL: DFT and dispersion Message-Id: <-45763-111028071708-22520-oRX/Z90C31m27zPSkQ0Tgw * server.ccl.net> X-Original-From: "Stefan Grimme" Date: Fri, 28 Oct 2011 07:16:37 -0400 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