A Sturmian Approach to Photoionization of Molecules

C. M. GRANADOS-CASTRO; C. M. GRANADOS-CASTRO, L. U. ANCARANI, G. GASANEO, D. M. MITNIK; G. GASANEO; D. M. MITNIK

Electron Correlation in Molecules: ab initio Beyond Gaussian Quantum Chemistry

Elsevier

Año: 2016; p. 3 - 57

An accurate theoretical description of photoionization processes is necessary in order to understand a wide variety of physical and chemical phenomena and allows one to test correlation effects of the target. Compared to the case of many-electron atoms several extra challenges occur for molecules. The scattering problem is generally multicenter and highly noncentral. The molecular orientation with respect to the polarization of the radiation field must also be taken into account. These features make the computational task much more cumbersome and expensive than for atomic targets. In order to calculate cross sections, one needs to describe the ejected electron with a continuum wavefunction with appropriate Coulomb asymptotic conditions. Making a number of initial approximations, many different theoretical/numerical methods have been proposed over the years. However, depending on the complexity of the molecule, agreement among them is not uniform and many features of the experimental data are not so well reproduced. This is illustrated through a number of examples. In order to have a global theoretical overview, we present a survey of most of the methods available in the literature, indicating their application to different molecules. Within a Bornâ??Oppenheimer, one-center expansion and single active electron approximation, we then introduce a Sturmian approach to describe photoionization of molecular targets. The method is based on the use of generalized Sturmian functions for which correct boundary conditions can be chosen. This property makes the method computationally efficient, as illustrated with results for H2O, NH3, and CH4.