title: Optimization of numerical orbitals using the Helmholtz kernel.
abstract: We present an integration scheme for optimizing the orbitals in numerical electronic structure calculations on general molecules. The orbital optimization is performed by integrating the Helmholtz kernel in the double bubble and cube basis, where bubbles represent the steep part of the functions in the vicinity of the nuclei, whereas the remaining cube part is expanded on an equidistant three-dimensional grid. The bubbles' part is treated by using one-center expansions of the Helmholtz kernel in spherical harmonics multiplied with modified spherical Bessel functions of the first and second kinds. The angular part of the bubble functions can be integrated analytically, whereas the radial part is integrated numerically. The cube part is integrated using a similar method as we previously implemented for numerically integrating two-electron potentials. The behavior of the integrand of the auxiliary dimension introduced by the integral transformation of the Helmholtz kernel has also been investigated. The correctness of the implementation has been checked by performing Hartree-Fock self-consistent-field calculations on H2, H2O, and CO. The obtained energies are compared with reference values in the literature showing that an accuracy of 10-4to 10-7Ehcan be obtained with our approach.
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
authors.forename: Eelis
authors.identifier: 000000024850430X
authors.initials: E
authors.lastname: Solala
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
authors.forename: Sergio A
authors.initials: SA
authors.lastname: Losilla
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
authors.forename: Dage
authors.identifier: 0000000223679277
authors.initials: D
authors.lastname: Sundholm
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
authors.forename: Wenhua
authors.identifier: 0000000298823384
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
authors.forename: Pauli
authors.identifier: 0000000342809230
authors.initials: P
authors.lastname: Parkkinen