Klimenko T. Coupled-cluster theory of excited and perturbed electronic states

Object of study: diatomic molecular systems: BH, FH, LiH, Li2, O2, pi-conjugated molecules. The purpose of the study - set the advantages of the concept of a fixed state in СС multireference theory in calculations of electronically excited states of small molecules at the level of experimental accuracy. Develop a semi empirical version of the CC theory to solve the problem of electron correlation treatment in calculations of the parameter of pi-conjugated systems perturbation with electric field. Research methods and apparatus - ab initio and semi empirical methods of quantum chemistry, software package GAMESS; software package CLUSTER; author's software package of numerical data processing of PES and solutions of the radial Schrodinger equation (HERZBERG); author's software package for calculation of the dipole (hyper)polarizabilities of conjugated molecules in the pi-electron approximation (pi-CC). Theoretical and practical results - developed a semi empirical variant of coupled cluster theory for solving the problem of electron correlation treatment in calculations of the parameter of pi-conjugated systems perturbation with electric field. The developed ab initio method for calculation and analysis of the potential energy surface of diatomic systems provides highly accurate estimates of the spectral characteristics of molecules in the ground and electronically excited states. Novelty - a numerical and analytical forms of CASCCSD adiabatic potential energy curves for several diatomic molecules for the ground and electronically excited states were obtained. The method of the given (fixed) state CASCCSD calculations of electronically excited states of small molecules was detailed. Software package HERZBERG for analytical processing of the numerical curves of PES was created and tested. It was established significant efficacy of the CC (in particular, in the unrelaxed version of the theory) in the study of nonlinear-optical properties of conjugated molecules. It was created the appropriate software package for the pi-electron calculations (pi-CC). The degree of implementation - implemented in the educational process. Field (area) of use - physical chemistry.