Theoretical Method Study On Some Types Of Noncovalent Interactions

Noncovalent interactions play important roles in various fields,such as physics,chemistry,material,biology,etc,and precise description of intermolecular interaction energy is essential for theoretical research and application of noncovalent interaction.However,it is generally difficult to accurately measure the intermolecular interaction energy through experimental methods.In recent decades,theoretical calculation methods are rapidly development and widely used.In this thesis,A24 test sets,cation-πsystems and 21noncovalent interaction complexes involvingπ-system are selected,and calculation accuracy and computational efficiency of different theoretical methods in calculating interaction energy are assessed comprehensively and systematically.In A24 test sets,the calculation accuracy of interaction energy by using random phase approximation（RPA）with various basis sets（Dunning’s correlation-consistent aug-cc-pVnZ basis sets and atom-centered orbital NAO-VCC-nZ basis sets）are assessed.The results show that RPA method is suitable for describing noncovalent interaction systems.Different types of basis sets has no significant impact on the calculation errors of RPA method.As for the good performance of RPA method in A24 test sets,we further select six typical cation-πsystems(Li⁺,Na⁺,Be²⁺,Mg²⁺,Al⁺,NH₄⁺-C₆H₆)to study,which are electrostatic-dominated.B3LYP,MP2,CCSD（T）,QCISD（T）,CCSD（T）/CBS and RPA methods are selected for assessment.The results show that the strength of the cation–benzene interactions is observed in the order of Be²⁺>Mg²⁺>Li⁺>Al⁺>Na⁺>NH₄⁺.In terms of calculating interaction energy,B3LYP and MP2 methods perform worse than the other theoretical calculation methods.The calculation accuracy of CCSD（T）and QCISD（T）methods are at same level and perform well.The calculation precision of RPA method is similar to that of CCSD（T）and QCISD（T）,while in terms of time consumption,RPA method is significantly shorter than that of CCSD（T）and QCISD（T）methods.We further select 21 noncovalent interactions complexes ofπ-system to study in depth.They are classified as electrostatic-dominated,dispersion-dominated and mixed interactions,respectively,which basically involves important noncovalent interaction types.The calculation accuracy of intermolecular interaction energy of nine theoretical methods（MP2,M06-2X-D3,ωB97XD,PBE-D3（BJ）,RPA,RPA+SE,RPA+rSE,RPA+SOSEX,rPT2）with aug-cc-pVTZ basis set are assessed.The results show that in the case of electrostatic dominated systems,besides RPA+SE method,all RPA-based methods perform better than that of MP2 and DFT-D.For RPA-based methods,there is no any improvement using larger aug-cc-pVQZ basis set.In the dispersion-dominatedπ-systems,the performance of dispersion-corrected DFT method is the most perfect.In the mixedπ-systems,all theoretical methods except standard RPA are applicable,especially MP2 and rPT2 with significant advantages.Moreover,for the dispersion-dominated and mixed-interaction systems,the calculation accuracy of RPA methods can be improved by using larger aug-cc-pVQZ basis set.Comparing with the standard RPA method,the calculation accuracy of intermolecular interaction energy can be remarkably improved by taking into account single excitation or exchange effects in the beyond-RPA methods（RPA+SE,RPA+rSE,RPA+SOSEX,rPT2）.