Modeling Positrons in Molecular Electronic Structure Calculations with the Nuclear-Electronic Orbital Method

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• 作者：Paul E. Adamson ; Xiaofeng F. Duan ; Larry W. Burggraf ; Michael V. Pak ; Chet Swalina ; Sharon Hammes-Schiffer
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：February 14, 2008
• 年：2008
• 卷：112
• 期：6
• 页码：1346 - 1351
• 全文大小：109K
• 年卷期：v.112,no.6(February 14, 2008)
• ISSN：1520-5215

文摘

The nuclear-electronic orbital (NEO) method was modified and extended to positron systems for studyingmixed 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 correspondingto the single-configuration mixed positronic-electronic wavefunction, minimized with respect to the molecularorbitals 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 activespace self-consistent-field (NEO-CASSCF) methods. In addition to implementing these methods for positronicsystems, 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-MP2and NEO-FCI energies and annihilation rates. The effects of basis set size on NEO-MP2 and NEO-FCIcorrelation energies and annihilation rates were compared. Even-tempered electronic and positronic basissets were also optimized for the e⁺LiH molecule at the NEO-MP2 level and used to compute the equilibriumbond length and vibrational energy.