Results 1 - 10 of 12
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[en] The adiabatic correction for the hydrogen-antihydrogen interaction in the ground state has been calculated using the Born-Handy method. The variational wavefunction was a linear combination of explicitly correlated Gaussian functions. It has been found that the correction grows rapidly for the nuclear separation approaching the critical distance. It is hypothesized that it becomes infinite at the point where the bound-state solution of the leptonic Schroedinger equation with fixed nuclei changes to a continuum wavefunction. This effect is nonphysical and means that there is no reasonable way to extend the adiabatic ground-state potential energy curve below the critical distance in a strict manner
[en] Inelastic collisions with hydrogen molecules are claimed to be an important channel of antihydrogen Hbar losses (Armour and Zeman 1999 Int. J. Quantum Chem. 74 645). In the present work, interaction energies for the H2-Hbar system in the ground state have been calculated within the Born-Oppenheimer approximation. The leptonic problem was solved variationally with the basis of explicitly correlated Gaussian functions. The geometry of H2 was fixed at equilibrium geometry and the Hbar atom approached the molecule from two directions-along or perpendicularly to the bond axis. Purely attractive potential energy curve has been obtained for the first nuclear configuration, while a local maximum (lower than the energy at infinite separation) has been found for the second one
[en] 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-p-bar pair has been established to be 0.744 Bohr. (author)
[en] The values of electron-positron coalescence, moments of distribution of the leptonic densities and electron-electron coalescence have been computed for the H-H-bar and He-H-bar systems. At selected values of the internuclear distances, maps of the electron-positron contact density have been prepared. The wavefunctions came from earlier variational calculations. This work is a step towards description of the annihilation of light particles in atom-antiatom collisions
[en] The order of low-energy states of six-electron harmonium is uncertain in the case of strong correlation, which is not a desired situation for the model system being considered for future testing of approximate methods of quantum chemistry. The computational study of these states has been carried out at the frequency parameter ω = 0.01, using the variational method with the basis of symmetry-projected, explicitly correlated Gaussian (ECG) lobe functions. It has revealed that the six-electron harmonium at this confinement strength is an octahedral Wigner molecule, whose order of states is different than in the strong confinement regime and does not agree with the earlier predictions. The results obtained for ω = 0.5 and 10 are consistent with the findings based on the Hund’s rules for the s2p4 electron configuration. Substantial part of the computations has been carried out on the graphical processing units and the efficiency of these devices in calculation of the integrals over ECG functions has been compared with traditional processors.
[en] The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection.
[en] The positions and widths of six resonances in the positron−helium system, for the electronic spin singlet state, have been computed using the stabilization method. The penetrable, parameter-dependent confining potential has been included in the Hamiltonian, and the energy eigenvalues have been obtained in the optimized, fixed basis of explicitly correlated Gaussian functions. Apart from four already known resonances below the threshold for the formation of positronium in its first excited state, a new one has been revealed below the energy of the state of the helium atom. The existence of the resonance formed by positron attachment to a doubly excited helium atom in the electron configuration has also been confirmed. (paper)
[en] Potential energy curves for interactions of antihydrogen atoms with singlet and triplet states of helium atom and helium cation have been calculated within the adiabatic approximation. The leptonic Schroedinger equation was solved variationally with the basis of explicitly correlated Gaussian functions. Adiabatic corrections have been calculated with the Born-Handy method. For the He(23S)-Hbar and He+- Hbar systems, critical distances have been found to be below 1.7 bohr and 1.0 bohr and the rearrangement cross sections have been computed with the semiclassical method. The possible existence and structure of complex atomcules is discussed
[en] The beryllium atom exhibits a significant response to an external electric field. The electric dipole hyperpolarizability of this atom has been calculated within the variation–perturbation scheme, using the basis of explicitly correlated Gaussian functions. Minimization of the fourth-order Hylleraas functional has yielded a result accurate to approximately 0.1%. The influence of various model confining potentials of spherical symmetry on beryllium's response functions is discussed within the same formalism. (paper)
[en] Method of construction of wave functions approximating eigenfunctions of the L^2 operator is proposed for high angular momentum states of few-electron atoms. Basis functions are explicitly correlated Gaussian lobes, projected onto irreducible representations of finite point groups. Variational calculations have been carried out for the lowest states of lithium atom, with quantum number L in the range from 1 to 8. Nonrelativistic energies accurate to several dozens of nanohartree have been obtained. For 22P, 32D, and 42F states they agree well with the reference results. Transition frequencies have been computed and compared with available experimental data