I have done a couple of calculations with this dispersion corrections and range separated functionals. The complex under study is Cinnamic---DMSO from XRD studies, where the ethylene group is 3.4 Angstroems from the S of DMSO (dimethylsulfoxide). The LMO-EDA ends up with reasonable energies, except for polarization energy that is way out of range
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ALL BASIS SET HARTREE KCAL/MOL
------------- wP57X-D / TZV
ELECTROSTATIC ENERGY ES= 35.155915 22060.69 kCal/mol ??
EXCHANGE ENERGY EX= 0.001502 0.94
REPULSION ENERGY REP= 0.020100 12.61
POLARIZATION ENERGY POL= -35.152773 -22058.72 kCal/mol ??
DFT DISPERSION ENERGY DISP= -0.008141 -5.11
TOTAL INTERACTION ENERGY HF OR DFT E= 0.016604 10.42
However using MP2 I get reasonable energies.
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ALL BASIS SET HARTREE KCAL/MOL
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ELECTROSTATIC ENERGY ES= -0.006687 -4.20
EXCHANGE ENERGY EX= -0.015563 -9.77
REPULSION ENERGY REP= 0.025771 16.17 kCal/mol
POLARIZATION ENERGY POL= -0.002422 -1.52 kCal/mol
MP2 DISPERSION ENERGY DISP= -0.005410 -3.40
TOTAL INTERACTION ENERGY HF OR DFT E= 0.001099 0.69
TOTAL INTERACTION ENERGY MP2 E= -0.004312 -2.71
Can anyone suggest a reason for that? Does anybody have a reference for H-bonds?
Thanks.
Article Energy Decomposition Scheme Based on the Generalized Kohn-Sham Scheme
You are using a rather obscure density functional: I don't recognise what part is exchange and what part is correlation. Before you start running off on the plethora of density functionals out there on the market, at least start with the greatly overused but at least well tested B3LYP. (Was your density functional maybe wB97XD?)
It is also not clear how you set up MP2. Probably MP2 gave you a better answer because it helps deal with polarisation.
Moreover, the basis set should at least have polarisation (TZVP), not TZV.
Anyway, if you demand high accuracy with molecular orbital calculations, your are going to have to spend a lot more money than TZVP can give you. TZVP might be ok for optimisating the geometry, but this is not for high accuracy calculations.
You need to study the functionals (what they aim at), select several that fit to your wavelength of interest, and test them with your problem to see how they really work. This is also true of basis sets. Sometimes, 6-31G* or TZVP is enough, but you have to find out and it depends on what you really want to know and how much accuracy you demand. You should also consider some expensive basis sets like cc-pVTZ and its derivatives aug and so forth.
You should understand that whereas QM is powerful and is informative, we have not arrived on the subject of high precision and accuracy, except maybe for very select and simple problems.
Dear Victor,
Are you sure that you used wp97xd?!! functional.I have never heard. If one assume you used wb97xd functional your unreasonable electrostatic may show there is something wrong with your input file, maybe you assigned an atom of one monomer to the other one. Also, I think sticking to a decomposition scheme is not a good decision I suggest you applying symmetry-adapted perturbation theory.
Dear Victor, I've got the same result with that functional. Unreasonable high values for electrostatic and polarization. Could you solve your problem?
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