Calculation of photoionization differential cross sections using complex Gauss‐type orbitals. Issue 23 (15th June 2017) - Matsuzaki, Rei
Abstract : Accurate theoretical calculation of photoelectron angular distributions for general molecules is becoming an important tool to image various chemical reactions in real time. We show in this article that not only photoionization total cross sections but also photoelectron angular distributions can be accurately calculated using complex Gauss‐type orbital (cGTO) basis functions. Our method can be easily combined with existing quantum chemistry techniques including electron correlation effects, and applied to various molecules. The so‐called two‐potential formula is applied to represent the transition dipole moment from an initial bound state to a final continuum state in the molecular coordinate frame. The two required continuum functions, the zeroth‐order final continuum state and the first‐order wave function induced by the photon field, have been variationally obtained using the complex basis function method with a mixture of appropriate cGTOs and conventional real Gauss‐type orbitals (GTOs) to represent the continuum orbitals as well as the remaining bound orbitals. The complex orbital exponents of the cGTOs are optimized by fitting to the outgoing Coulomb functions. The efficiency of the current method is demonstrated through the calculations of the asymmetry parameters and molecular‐frame photoelectron angular distributions of H 2 + and H 2 . In the calculations of H 2 , the static exchange and random phase approximations are employed, and the dependence of the results on the basis functions is discussed. © 2017 Wiley Periodicals, Inc. Abstract : A practical calculation method of molecular photoionization differential cross sections using complex Gauss‐type orbitals (cGTOs) is developed based on the complex basis function method. Effective complex basis functions are determined by fitting a linear combination of cGTOs to outgoing Coulomb functions. The photoionization partial cross sections, the asymmetry parameters, and the molecular‐frame photoelectron angular distributions of H 2 + and H 2 are calculated to demonstrate the efficiency. The RPA is applied to H2 .