Dispersion Correction To The B3LYP Calculations Of Intermolecular Interactions

The calculation of intermolecular interaction energy is an important content in the fields of biological processes,drug design,catalytic processes and material chemistry.Using quantum chemistry to calculate the intermolecular interaction energy is an important application of quantum mechanical methods.In the theoretical calculation methods of quantum chemistry,the Coulomb correlation approximation not considered by the HF method is expressed by the density functional method,and the accuracy of the calculation is improved,and this method is selected to be applied to the calculation of the relevant system.Among them,the B3LYP was used widely.The B3LYP is not accuracy in calculating the intermolecular interaction energy,and even leads to complete error.It is because that the B3LYP can not accurately describe the dispersion effect which plays an important role in calculating intermolecular interaction energy.This paper improves the accuracy of B3LYP in calculating the interaction between molecules by adding a dispersion correction term to solve the problem that B3LYP can not deal with the dispersion effect.In this paper,we use the B3LYP functional to combine the four basis sets to calculate the intermolecular interactions of the S66 database.The supramolecular method was used to calculate the intermolecular interactions by considering the Basis Set Superposition Error(BSSE),and the influence of the BSSE and the basis set on the intermolecular interactions was analyzed.According to the characteristics of the atom and the configuration relationship of the dimer,the fitting dispersion correction formula is as follows:Where rAB is the distance of the atoms in the two molecules,rAe is the effective radius of the A atom,nvAe is the effective valence electron number of the A atom,?A is the electronegativity of the A atom,and the B atom is the same,the dispersion formula needs to be fitted four coefficients.The dimers in the S66 database can be divided into three categories:electrostatic(hydrogen bonding,23 complexes),dispersion(23),and mixed(dispersion/electrostatic,20).First,all the dimers were fitted The dispersion correction formula coefficients were C1=0.1,C2=1,C3=0.5,C4=2.0,C5=3.0,and MAE=0.62 kcal/mol.For each type of dimer,the coefficients were C1=0.1,C2=1,C3=1.4,C4=2.0,C5=3.0,and MAE=0.47 kcal/mol for the electrostatic dimer.For dispersive dimers,the coefficients are C1=0.07,C2=1,C3=0.4,C4=2.4,C5=9.0,MAE=0.65 kcal/mol.For mixed dimers,the coefficients are C1=0.1,C2=1,C3=0.5,C4=2.0,C5=3.0,MAE=0.34 kcal/mol.In this paper,the dispersion correction formula is proposed to fit the coefficients of different types of dimers in the S66 database,and more accurate results are obtained,which solves the defect of the intermolecular interaction of the B3LYP functional calculation.