I am working with a hydrogen bond receptor theoretically. Actually, I want to find IR, NMR, NBO charge, HOMO-LUMO energy gap, BSSE correction, PES scan, Theoretical fluorescence spectra using GAUSSIAN 09W theoretically for beta-carboline type molecule in a WORKSTATION series computer. Which would be the best basis set and theoretical model for my system?
There are a number of studies providing different answers. Here is one which is quite extensive.
J. Chem. Theory Comput., 2007, 3 (2), pp 407–433
Just a comment. Fluorescence is a processe with life-time in order of tens "fs", whereas H-bonds shows average life-time in order of the some "ps". If Born-Oppenheimer approximation can be applied, probably both processes have not correlation.
Hi Paul
I think cc-pvtz would be best but much expensive so you can go for less expensive basis set. If you want to, then you can also go for compound methods. There you wouldn't need to be worried about this at all and it also can compete with cc-pvtz quite good within less time.
Dear Paul:
from my computational experience I think that the best basis set to obtain IR, optimized geometries, BSSE, etc. to optimize a geometry is the B3LYP/cc-pVTZ —efficiency between computational time/electronic energy— if your system have internal HB, or B3LYP/aug-cc-pVTZ if your system have HB inter-monomers. If you use cc-pVQZ only increase your computational cost but the resultant energy is slightly better than –TZ basis set.
You have papers by Scuseria, Parrinello, etc. where you can read about HB systems.
Regards
Hi Paul!
For the geometry optimization the B3LYP/CBSB7 method would be enough (it's less expensive and provides reliable geometry), then you can calculate the different spectra at higher basis sets (cc-pVTZ or QZ) precisely. Besides the BSSE correction, don't forget to take account of the relaxation therm.
Good luck!
See recent papers by Rozenberg, Loewenschuss and Nielsen for computations on various H-bonded complexes and clusters
See recent papers by Masoud Mirzaei and Antonio Frontera for computations on various H-bonded complexes and clusters
Thanks to all of you for your valuable answer. I am grateful to all of you.
Can you please say so the best solvent model for the same HB calculation in acetonitrile. I am confused between COSMO and IEFPCM.
Dear Suvendu:
the fist step in DFT is optimize with HF but for to confirm that all harmonic frequencies are real in the IR spectrum is necessary to carry out the calculations with other high level method.
Which is the best basis set, theoretical model for hydrogen bond claculation using Gaussian?
hi
basis set= B3LYP/6-311++G**
for calculating the H. Bonding I recommend to use either DFT such as B3LYP or B3P86 and MP2 using a basis set 6-311+G(d)/6-311++G(df) based on the system you are study. There is reference for that in computational and theoretical chemistry 2011
Regarding basis sets, you may want to consider Jensen's polarization-consistent (pc) basis sets, which are optimized for HF/DFT calculations and probably give more "accuracy per basis function" than Dunning's cc-pV*Z basis sets (which are designed for explicitly correlated methods as MPn or CC).
For the present problem, the aug-pcseg-2 appears appropriate, an augmented valence-TZ basis set.
The pc basis sets are not available in Gaussian09 (in Dalton 2015, most of them are), but can be downloaded in GAussian format from the EMSL basis-set exchange https://bse.pnl.gov/bse/portal.
For more information, see
Frank Jensen, Unifying General and Segmented Contracted Basis Sets. Segmented Polarization Consistent Basis Sets., Journal of Chemical Theory and Computation 10, 1074-1085 (2014)
and references therein.
As A.S.A. suggests above and in my own experience, the B3LYP functional does not handle weak intermolecular well. Depending on the size of the system, you may be able to get by with M06-2X.
Thanks to all of you. But, when I am using WB97XD there is another new option of matching case. I ignored it without selecting anything. Am I Ok?
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