title: Modeling positrons in molecular electronic structure calculations with the nuclear-electronic orbital method.
abstract: The nuclear-electronic orbital (NEO) method was modified and extended to positron systems for studying mixed positronic-electronic wavefunctions, replacing the mass of the proton with the mass of the positron. Within the modified NEO framework, the NEO-HF (Hartree-Fock) method provides the energy corresponding to the single-configuration mixed positronic-electronic wavefunction, minimized with respect to the molecular orbitals expressed as linear combinations of Gaussian basis functions. The electron-electron and electron-positron correlation can be treated in the NEO framework with second-order perturbation theory (NEO-MP2) or multiconfigurational methods such as the full configuration interaction (NEO-FCI) and complete active space self-consistent-field (NEO-CASSCF) methods. In addition to implementing these methods for positronic systems, strategies for calculating electron-positron annihilation rates using NEO-HF, NEO-MP2, and NEO-FCI wavefunctions were also developed. To apply the NEO method to the positronium hydride (PsH) system, positronic and electronic basis sets were optimized at the NEO-FCI level and used to compute NEO-MP2 and NEO-FCI energies and annihilation rates. The effects of basis set size on NEO-MP2 and NEO-FCI correlation energies and annihilation rates were compared. Even-tempered electronic and positronic basis sets were also optimized for the e+LiH molecule at the NEO-MP2 level and used to compute the equilibrium bond length and vibrational energy.
authors.affiliation: Air Force Institute of Technology, Wright-Patterson AFB, Ohio 45433, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Adamson
authors.forename: Xiaofeng F
authors.initials: XF
authors.lastname: Duan
authors.forename: Larry W
authors.initials: LW
authors.lastname: Burggraf
authors.forename: Michael V
authors.initials: MV
authors.lastname: Pak
authors.forename: Chet
authors.initials: C
authors.lastname: Swalina
authors.forename: Sharon
authors.initials: S
authors.lastname: Hammes-Schiffer