Krzysztof Strasburger

Adiabatic positron affinity of LiH

The equilibrium geometry of the positronic molecule e+LiH has been found, using the explicitly correlated Gaussian functions in the variational calculations. The value of the adiabatic positron affinity of lithium hydride has been calculated. The influence of the geometry relaxation on the properties of the system has also been shortly discussed.

Binding energy, structure, and annihilation properties of the positron-LiH molecule complex, studied with explicitly correlated Gaussian functions

The energy and two-photon annihilation rate of the complex of the LiH molecule with a positron have been calculated for the equilibrium geometry of LiH in the gas phase, using the explicitly correlated Gaussian basis set. The resulting energy of e+LiH (−8.104 850 hartree) is the lowest obtained to date. The binding energy of the positron in this system has been predicted to be at least 34.401 mhartree, and the annihilation rate has been estimated to be 1.26 ns−1. Maps of the electron, positron, and contact (electron–positron) densities have been prepared.

QUANTUM CHEMICAL STUDY OF SIMPLE POSITRONIC SYSTEMS USING EXPLICITLY CORRELATED GAUSSIAN FUNCTIONS - PSH AND PSLI+

The electronic structure of positronium hydride has been studied using explicitly correlated Gaussian functions. The resulting energy constitutes new upper bound to the exact nonrelativistic energy of PsH within the Born–Oppenheimer approximation. The two photon annihilation rate was computed using the optimized wave function. Preliminary results for the positron bonded with the lithium atom indicate the stability of this system against the dissociation into Li+ cation and Ps atom.

Configuration interaction study of the positronic hydrogen cyanide molecule

Using the configuration interaction approach, we have revealed that the positronic HCN molecule is energetically stable. The dependency of the positron binding energy on the molecular basis set was studied as well. The use of the basis set constructed explicitly for the sake of polarizability calculations shows that the binding energy of positron to HCN can be as big as about 1.3 mhartree. This article is dedicated to Professor Andrzej J. Sadlej on the occasion of his 65th birthday anniversary.

Quantum chemical study on complexes of the LiH molecule with e+, Ps and Ps− including correlation energy

Abstract SCF and CI energies of the LiH, LiH − , e + LiH, LiHPs and LiHPs − systems have been evaluated in the extended basis set at the experimental geometry of LiH. Electron and positron affinities of the LiH molecule have been compared. The results indicate the importance of the correlation energy in positron-molecule complexes.

Positronic Formaldehyde—the Configuration Interaction Study

Positron binding to the formaldehyde molecule has been determined within the Hartree–Fock and configuration interaction approaches. Rough estimation of the positron affinity of formaldehyde, obtained with the CI method, is 684 micro-Hartree. Problems of building the appropriate positronic basis set in molecular calculations are discussed.

On the reliability of the SCF and CI wavefunctions for systems containing positrons

Abstract The energies and electron—positron collision probabilities for complexes of a positron with one- and two-electron atoms of variable nuclear charge have been studied. In the case of a one-electron atom quantum chemical calculations within the correlated functions approach have also been performed. The results obtained suggest that the energy of the complex can be reproduced relatively well at the CI level, but it requires the use of a flexible basis set. However, it is practically imposible to obtain reliable values of the collision probability. An alternative method of estimation of the electron—positron collision probability has been proposed. It is based on an equation relating the cusp value with the relevant collision probability.

Electric dipole (hyper)polarizabilities of spatially confined LiH molecule

In this study we report on the electronic contributions to the linear and nonlinear static electronic electric dipole properties, namely the dipole moment (μ), the polarizability (α), and the first-hyperpolarizability (β), of spatially confined LiH molecule in its ground X (1)Σ(+) state. The finite-field technique is applied to estimate the corresponding energy and dipole moment derivatives with respect to external electric field. Various forms of confining potential, of either spherical or cylindrical symmetry, are included in the Hamiltonian in the form of one-electron operator. The computations are performed at several levels of approximation including the coupled-cluster methods as well as multi-configurational (full configuration interaction) and explicitly correlated Gaussian wavefunctions. The performance of Kohn-Sham density functional theory for the selected exchange-correlation functionals is also discussed. In general, the orbital compression effects lead to a substantial reduction in all the studied properties regardless of the symmetry of confining potential, however, the rate of this reduction varies depending on the type of applied potential. Only in the case of dipole moment under a cylindrical confinement a gradual increase of its magnitude is observed.

The three-electron harmonium atom: The lowest-energy doublet and quadruplet states

Calculations of sub-μhartree accuracy employing explicitly correlated Gaussian lobe functions produce comprehensive data on the energy E(ω), its components, and the one-electron properties of the two lowest-energy states of the three-electron harmonium atom. The energy computations at 19 values of the confinement strength ω ranging from 0.001 to 1000.0, used in conjunction with a recently proposed robust interpolation scheme, yield explicit approximants capable of estimating E(ω) and the potential energy of the harmonic confinement within a few tenths of μhartree for any ω ≥ 0.001, the respective errors for the kinetic energy and the potential energy of the electron-electron repulsion not exceeding 2 μhartrees. Thanks to the correct ω → 0 asymptotics incorporated into the approximants, comparable accuracy is expected for values of ω smaller than 0.001. Occupation numbers of the dominant natural spinorbitals and two different measures of electron correlation are also computed.

Accurate Born–Oppenheimer potential energy curve for the hydrogen–antihydrogen system

The energy curve of the hydrogen–antihydrogen system has been calculated using the Rayleigh–Ritz variational method, with a basis of correlated Gaussian functions. The microHartree accuracy of Born–Oppenheimer energies of this system has been achieved for the first time for short internuclear distances. The new upper bound to the terminal distance of Ps binding by the p– pair has been established to be 0.744 Bohr.