We investigate a dimer of an organic molecule. It is linked together by two hydrogen bridges.
a) What is the best way to calculate the bonding energy of the dimer?
One possible approach is to optimize the geometries of the dimer and the monomer with classical DFT methods, let’s say B3LYP/6-311+G(d,p). The energy of the monomer is corrected with BSSE correction. The difference between (2x)monomer and dimer energy gives the bond energy of the hydrogen bond.
b) Is that correct?
c) How to do this type of calculation with modern dispersion-corrected DFT methods?
d) Which method / basis set combination would you propose?
Dear Uwe,
The consensus among computational chemists is that the correct approach to obtain an intermolecular interaction energy between two entities or more is using the counterpoise correction of Boys and Bernardi,. It is quite convincing to calculate the interaction energy between the two monomers as a difference of energies of AB and sum of A and B. In your case you should use the keyword "counterpoise=2" in Gaussian. Regarding the method and basis set; MP2 is advantageous over B3LYP in calculating intermolecular interactions, and the basis set could be chosen depending on the size of the compound.
Hoping this will be helpful,
Rafik
I can't help much for the theoretical viewpoint but my colleagues at the University of Nantes (C. Laurence, J.Y. Le Questel, J. Graton, ...) have a long experience concerning the experimental aspects, and made several test studies for the application of ab initio/DFT methods, for example:
- Can Quantum-Mechanical Calculations Yield Reasonable Estimates of Hydrogen-Bonding Acceptor Strength? The Case of Hydrogen-Bonded Complexes of Methanol_J. Phys. Chem. A, 2011, 115 (47), pp 13975–13985
Hydrogen-Bond Acidity of OH Groups in Various Molecular Environments (Phenols, Alcohols, Steroid Derivatives, and Amino Acids Structures): Experimental Measurements and Density Functional Theory Calculations_J. Phys. Chem. A, 2013, 117 (49), pp 13184–13193
A DFT-D evaluation of the complexation of a molecular tweezer with small aromatic molecules_Chemical Physics Letters-Volume 522, 19 January 2012, Pages 11–16
Molecular Tweezers in Host–Guest Complexes: A Computational Study through a DFT-D Approach_J. Phys. Chem. C, 2012, 116 (43), pp 23067–23074
and many others.
Your ans to B is yes. as to which method is the best..I will say use MP2 methods with big basis sets.
Usually people optimize the structure at B3LYP and then use MP2 or MP3 level of theory for calculation of interaction energy.
You can calculate the difference between Gibbs Free Energies for dimer (many-particle system) and separate molecules using on-line "Thermodynamics: Heat Capacity, Enthaly, Entropy, Gibbs Free Energy, log(BCF)" software at www.chemosophia.com
Is it possible to calculate the electrostatic, exchange-repulsion, dispersion and induction energies using Gaussian?
Muthuraja Perumal Gaussian can't partition the interaction energy of a hydrogen bond you need special programs such Molpro (SAPT) or NBO. They are certainly some other program too
Thanks for you information V.P.N. Nziko, what would be the input for that programs? shall we use the cif files or some other formats required? Do you have any idea? if so kindly post it!!
You can use the PIXEL method (Phys. Chem. A 2011, 115, 11179– 11186.) to calculate decomposed interaction energy. It is easy, less time consuming.
Thank you for your message Subhrajyoti Bhandary. Do you have any idea about using this PIXEL calculations? Please post the details if possible. Meanwhile, I also read the article you mentioned too...
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