CCL:G: DFT and dispersion

 Sent to CCL by: Arne Dieckmann [adieckma###googlemail.com]
 Dear Lars,
 my systems resemble the active sites of enzymes, so dispersion effects will play
 a major role if a certain number of catalytic side chains are present. What
 other dispersion corrected functional would you recommend (apart from TPSS)? I
 guess you are more experienced with this than I am.
 Thanks,
 Arne
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Dr. Arne Dieckmann
 Houk Research Lab
 University of California, Los Angeles
 email: adieckma- -googlemail.com
 On Oct 27, 2011, at 11:26 PM, Dr. Lars Goerigk lars.goerigk:+:chem.usyd.edu.au
 wrote:
 >
 > Sent to CCL by: "Dr. Lars Goerigk" [lars.goerigk a
 chem.usyd.edu.au]
 > Dear Arne,
 >
 > I guess it depends entirely on your system to decide whether a D correction
 with M06-2X has an impact on the geometries or not. As I do not know the system,
 I cannot say how much of the intramolecular dispersion effects are covered by
 M06-2X. I also do not have much experience with M06-2X-D3 geometry
 optimizations. However, I assume that a system of more than 50 atoms should show
 significant intramolecular dispersion effects, that of course also influence the
 relative energies between conformers.
 >
 > Personally, I would always include a dispersion correction to be on the
 safe side. Maybe you could run a test calculation on one of the systems with
 M06-2X and another dipsersion-corrected functional (TPSS should be in general
 faster, of course). Then you can maybe see the effect on your system and can
 make a final decision.
 >
 > But maybe other users, who are reading this, have already done such a
 comparison and can give you also some recommendations.
 >
 > Cheers,
 > Lars
 >
 > On 28/10/2011 4:15 PM, Arne Dieckmann adieckma(-)googlemail.com wrote:
 >> Sent to CCL by: Arne Dieckmann [adieckma(-)googlemail.com]
 >> Dear Lars,
 >>
 >> thanks for your immediate reply. I know about the differences between
 the Minnesota functionals and the DFT-D3 method. This is why I wanted to augment
 their mid-range dispersion with the long range dispersion your former group
 developed. Do you know if TPSS with D-corrections produces significantly
 different geometries than M06-2X without D-corrections? How much do geometries
 of molecules (>= 50 atoms) change in general? I am just wondering if it will
 be sufficient to optimize with M06-2X and apply the single point D-corrections.
 >>
 >> 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?
 >>
 >>
 >> Thanks again,
 >> Arne
 >>
 >> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 >> Dr. Arne Dieckmann
 >> Houk Research Lab
 >> University of California, Los Angeles
 >> email: adieckma+*+googlemail.com
 >>
 >>
 >> On Oct 27, 2011, at 5:28 PM, Dr. Lars Goerigk
 lars.goerigk{}chem.usyd.edu.au wrote:
 >>
 >>> Sent to CCL by: "Dr. Lars Goerigk"
 [lars.goerigk(~)chem.usyd.edu.au]
 >>> Dear Arne,
 >>>
 >>> M06-2X was fitted to noncovalently bound systems in their
 equilibrium geometries and due to that fit it somehow incorporates medium-range
 dispersion interactions. However, as also discussed in the literature, it is
 expected that the asymptotic long-range behavior is still not correct and that
 it can also benefit from dispersion corrections.
 >>> On the issue DFT-D3 in combination with the Minnesota functionals
 you can refer to PCCP 2011, 13, 6670. There, the parameters for DFT-D3 for those
 functionals were published and discussed.
 >>>
 >>> DFT-D2 parameters for the Minnesota functionals were published by
 the Martin group in JPCA 2008, 112, 12868. The s6 had to be smaller than unity,
 though, which still does not give the correct asymptotics, opposed to DFT-D3,
 where it was fixed to unity.
 >>>
 >>> If you have the Gaussian code available you could try to implement
 DFT-D3 (based on the code Stefan Grimme made available on his website).
 >>> If you do not have the code, you would have to use DFT-D2. Please
 note that in G09 Rev A, DFT-D2 only works with B97-D and omega-B97X-D.
 >>> That bug was fixed however and in Rev. B01 and higher you can now
 also use DFT-D2 for those functionals, which are mentioned in Grimme's DFT-D2
 paper from 2006 (i.e. also for B3LYP, TPSS, PBE, BP86).
 >>> You have to use the IOp(3/124=3) then. In combination with
 IOp33(3=3) you also get a printout to check, if the correct s6 value was
 applied.
 >>> Other functionals are not supported and I do not know if it is
 possible to read in an s6 specified by the user (maybe you should contact the
 Gaussian support to find that out). IOp(3/124=1)  adds the dispersion correction
 to any functional, but only with an s6=1, which is too large for the Minnesota
 functionals.
 >>>
 >>> If you can't use M06-2X, you could try TPSS in combination with
 D-corrections. Based on publications and my own experience, this gives very good
 structures.
 >>>
 >>> Another possibility would be to get ORCA, which is for free. I am
 not 100% sure if DFT-D3 is already implemented; have a look at the ORCA website
 for that.
 >>> You could also check if other programs have already implemented
 DFT-D3.
 >>>
 >>> I hope these information could help you.
 >>>
 >>> With best wishes,
 >>> Lars
 >>>
 >>> --
 >>> Dr. Lars Goerigk
 >>> School of Chemistry
 >>> The University of Sydney
 >>> Sydney, New South Wales 2006
 >>> Australiahttp://www.ccl.net/chemistry/sub_unsub.shtml>;
 >>
 >
 >
 > --
 > Dr. Lars Goerigk
 > School of Chemistry
 > The University of Sydney
 > Sydney, New South Wales 2006
 > Australiahttp://www.ccl.net/chemistry/sub_unsub.shtml>;
 >