Department of Chemistry, Purdue University, 560 Oval Dr, West Lafayette, IN 47907, USA.
Phys Chem Chem Phys. 2012 Jun 7;14(21):7780-6. doi: 10.1039/c2cp23994a. Epub 2012 Apr 10.
The exact ground-state energy and density of a molecule can in principle be obtained via Partition Density Functional Theory (PDFT), a method for calculating molecular properties from Kohn-Sham calculations on isolated fragments. For a given choice of fragmentation, unique fragment densities are found by requiring that the sum of fragment energies be minimized subject to the constraint that the fragment densities sum to the correct molecular ground-state density. We investigate two interrelated aspects of PDFT: the connections between fragment densities obtained via different choices of fragmentation, for which we find "near-additivity", and the nature of their corresponding fragment occupations. Whereas near-integer occupations arise for very large inter-fragment separations, strictly integer occupations appear for small inter-fragment separations. Cases where the fragment chemical potentials cannot be equalized lead to fragment occupations that lock into integers.
原则上，可以通过分区密度泛函理论（PDFT）获得分子的精确基态能量和密度，这是一种从孤立碎片上的 Kohn-Sham 计算来计算分子性质的方法。对于给定的碎片选择，通过要求碎片能量的总和最小化，同时满足碎片密度总和等于正确的分子基态密度的约束条件，可以找到唯一的碎片密度。我们研究了 PDFT 的两个相互关联的方面：通过不同的碎片选择获得的碎片密度之间的关系，我们发现了“近似可加性”，以及它们对应的碎片占据的性质。虽然在非常大的碎片间分离时会出现近整数占据，但在小的碎片间分离时会出现严格的整数占据。如果不能使碎片化学势相等，则会导致碎片占据锁定在整数上。
