Relativistic AB Initio calculations of interaction energies: formulation and application to ionic solids
Relativistic AB Initio calculations of interaction energies: formulation and application to ionic solids
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DOI：
10.1098/rsta.1986.0105
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发表时间：
1986-11
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通讯作者：
O. Abiniti;OF Calculations;I. N. T. E. R. A. C. T. I. O. N. Energi-I.-N.-T.-E.-R.-A.-C.-T.-I.-O.-N.-Energi-2257245236;S. Solid
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文献类型：
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作者：
O. Abiniti;OF Calculations;I. N. T. E. R. A. C. T. I. O. N. Energi-I.-N.-T.-E.-R.-A.-C.-T.-I.-O.-N.-Energi-2257245236;S. Solid
本文介绍了一个能对相互作用的原子物种进行完全相对论性从头计算的计算机程序所采用的理论和计算技术。如果物质是晶体中的离子，则得到离子固体的描述。如果这两种物质在其他方面是自由的，程序就产生一个双原子分子的波函数。分子波函数是核部分和价部分的反对称乘积。核心是自由原子的狄拉克-福克原子轨道的哈特里积。对能量的最大贡献来自内核轨道，每个轨道与所有其他轨道的重叠可以忽略不计。纯粹的原子内核能量对分子的结合能没有贡献，因此不需要计算分子能量的最大部分。外核由那些对分子形成没有显著影响的孤立原子的剩余封闭子壳层组成。所有剩余的轨道，至少包括自由原子的价Dirac-Fock原子轨道加上描述分子形成时电荷密度变化所需的进一步原子函数，用于构建价波函数。这可以考虑到价电子之间的相关性。所有的原子函数都有中心场的形式，径向部分用数值定义。这种构造分子波函数的方法避免了对大基组的需要，确保了狄拉克小分量与大分量具有正确的关系，并避免了基组叠加误差。该程序用于启动离子固体性质的非经验研究。结果表明，用自由离子波函数不能可靠地预测这些性质，用沃森壳模型来描述自由离子波函数与晶体内离子波函数之间不可忽略的差异也不能令人满意.结果表明，离子间色散吸引的重要性，但它是不令人满意的，以忽略这些吸引力的标准长程形式所产生的重叠的离子波函数的部分淬火。
The theory and computational techniques used in a computer program capable of performing fully relativistic ab initio electronic structure calculations for pairs of interacting atomic species are presented. If the species are ions in a crystal, a description of an ionic solid is obtained. If the two species are otherwise free, the program yields a wavefunction for a diatomic molecule. The molecular wavefunction is an antisymmetrized product of core and valence parts. The core is a Hartree product of the Dirac—Fock atomic orbitals of the free atoms. The largest contribution to the energy arises from the inner-core orbitals, each having negligible overlap with all other orbitals. The purely atomic inner-core energy does not contribute to the binding energy of the molecule, thus obviating the need to calculate the largest part of the molecular energy. The outer core consists of those remaining closed subshells of the isolated atoms that are not significantly affected on molecule formation. All the remaining orbitals, including at least the valence Dirac—Fock atomic orbitals of the free atoms plus further atomic functions needed to describe charge density changes upon molecule formation, are used to construct the valence wavefunction. This can be constructed to take account of correlation between the valence electrons. All atomic functions have central field form with the radial parts defined numerically. This method of constructing the molecular wavefunction avoids the need for large basis sets, ensures that the Dirac small components bear the correct relation to the large components and avoids basis set superposition errors. This program is used to initiate a non-empirical study of the properties of ionic solids. The results show that these properties cannot be reliably predicted by using free ion wavefunctions and that the Watson shell model for describing the non-negligible differences between free and in-crystal ion wavefunctions is not satisfactory. The results demonstrate the importance of inter-ionic dispersive attractions but show that it is not satisfactory to neglect the part quenching of the standard long-range form of these attractions arising from overlap of the ion wavefunctions.