Research On The Exact Calculation Method Of Quantum Chemistry For The Thermodynamic Function Of Intermolecular Interaction

The calculation of thermodynamic functions is of great significance in scientific research.The chemical reactions we studied or the formation of complexes were performed at a certain temperature（T）and pressure（P）.Therefore,in the calculat io n of numerous thermodynamic functions,the Gibbs free energy（ΔG）calculation appears to be the most important.It shows under certain thermodynamic conditions whether a macroscopic process can proceed spontaneously.At present,there are many experimental methods to determine the Gibbs free energy changeΔG of a process.Such as electromotive force method,quadrupole mass spectrometry and chromatography.However,it is experimentally difficult to determine theΔG during the interaction between molecules.Especially some unstable weak interaction systems or some electrical neutral systems.At present,quantum chemistr y calculation methods for the calculation of binding energy,such as CCSD（T）,can already achieve chemical accuracy under some large groups.The calculation of the thermodynamic function requires not only the calculation of the binding energy but also the vibration analysis of the molecule.Therefore,it is much more difficult to calculateΔG.For single-molecule problems,the prediction of vibration frequency is already quite accurate.However,the calculation ofΔG is still a problem for the intermolecular interactions.Although CCSD（T）+VPT2 is very accurate in calculating the frequency of molecular vibrations in the tetra-zeta group,this high-level post-SCF vibratio n analysis is very time-consuming and can only be used in small molecule systems;for slightly larger The system is difficult to achieve.In addition to the need to calculate the binding energy associated with the formation of atmospheric molecules in the study of atmospheric particle nucleation of multi-particle system,it is necessary to more accurately know the Gibbs free energy of the nucleation process.Therefore,it is extremely valuable to explore a precise and fast quantum chemical calculation method to solve the calculation ofΔG during the intermolecular interaction.In this paper,we use a series of 25 DFT calculation methods to test a series of hydrogen bonding,dispersion and inducing effects.At the same time,the combination calculation ofωB97X-V functional which is more accurate in calculation of binding energy and other different DFT calculation methods is investigated.The study found that the combined calculation method can significa nt ly improve the calculation accuracy.Especially the B3PW91-D3BJ+ωB97X-V combination method,the RMSE value can be maintained within 1kcal·mol^-1.