On the choice of a distributed basis set in calculations of transition-dipole moments in the one-determinant approximation

The so-called “asymptotic projection technique” developed in previous papers of the authors is applied to the calculation of electronic transition-dipole moments (TDMs) in the one-determinant approximation between states of the same spin and spatial symmetry. The basic equations of the method and specific features of their application to a TDM calculation are briefly discussed. The attention focusses on the choice of a finite one-particle basis set. For this purpose, two possible algorithms for constructing distributed basis sets are proposed. In the first of them, the construction is based on minimization of the Hartree–Fock energy $(E_{\mathrm{HF}})$ with respect to nonlinear basis set parameters. In the second case, the parameters are determined by minimizing the functional $E=E_{\mathrm{HF}}+E_{\mathrm{MP2}}$, which includes the electron correlation through the second order of Møller–Plesset perturbation theory $(E_{\mathrm{MP2}})$. On the whole, the results of calculations in both basis sets are in agreement with high-accuracy calculations performed by configuration interaction methods. The basis set adapted for $E=E_{\mathrm{HF}}+E_{\mathrm{MP2}}$ significantly improves the accuracy as compared to the basis set of the first type.