Time-dependent generalized-active-space configuration-interaction approach to photoionization dynamics of atoms and molecules

Abstract

We present a wave-function based method to solve the time-dependent many-electron Schrödinger equation (TDSE) with special emphasis on strong-field ionization phenomena. The theory builds on the configuration-interaction (CI) approach supplemented by the generalized-active-space (GAS) concept from quantum chemistry. The latter allows for a controllable reduction in the number of configurations in the CI expansion by imposing restrictions on the active orbital space. The method is similar to the recently formulated time-dependent restricted-active-space (TD-RAS) CI method [D. Hochstuhl, and M. Bonitz, Phys. Rev. A 86, 053424 (2012)]. We present details of our implementation and address convergence properties with respect to the active spaces and the associated account of electron correlation in both ground state and excitation scenarios. We apply the TD-GASCI theory to strong-field ionization of polar diatomic molecules and illustrate how the method allows us to uncover a strong correlation-induced shift of the preferred direction of emission of photoelectrons.

Inner-shell photoionization and core-hole decay of Xe and XeF2

“…Theoretical treatments of inner-shell photoionization and core-hole decays in atoms and molecules have been actively studied in the literature. [30][31][32][33][34][35][36][37][38][39] Both nonrelativistic [30][31][32][33][34][35][36][37][38] and relativistic 39 Hamiltonians have been used together with a variety of quantum-chemical methods, ranging from the configuration interaction singles method to highorder Green's function techniques. The limitation of standard Gaussian functions in describing the regions outside the molecule, which is relevant to the dynamics of photoionization and core-hole decays, has been noted and discussed.…”

Communication: Time-dependent optimized coupled-cluster method for multielectron dynamics

“…25,28 These codes share the same implementation for the basis-independent procedures [Eqs. (13), (14), (17)- (19), and (21)- (23)]. …”

“…See, e.g, Refs. [16][17][18][19] for TDCI methods using fixed orbitals and Ref. 15 for a broad review of ab initio wavefunction-based methods for multielectron dynamics.)…”

Instabilities and inaccuracies of multi-configuration time-dependent Hartree-Fock

“…Moreover, we suspect that other methods using time-dependent orbitals, like the time-dependent renormalized natural orbital theory [18] and orbital-adaptive time-dependent coupled-cluster [19], might show similar problems as all of these methods involve an inversion of the single-particle density matrix or equivalent operations. One contender for a replacement are CI-based methods with time-independent orbitals, like the time-dependent generalized-active-space configuration interaction (TD-GAS-CI) method [1,[20][21][22], due to their static Hilbert space. Another class of methods which have proven to be especially suited for Hubbard-like systems are based on the non-equilibrium Green function (NEGF) approach [14,[23][24][25].…”