Røeggen I
Department of Physics, University of Tromsø, 9037 Tromsø, Norway.
J Chem Phys. 2006 May 14;124(18):184502. doi: 10.1063/1.2192501.
The hexagonal close packed (hcp) and face centered cubic (fcc) structures of helium are studied by using a new ab initio computational model for large complexes comprising small subsystems. The new model is formulated within the framework of the energy incremental scheme. In the calculation of intra- and intersystem energies, model systems are introduced. To each subsystem associated is a set of partner subsystems defined by a vicinity criterion. In the independent calculations of intra- and intersystem energies, the calculations are performed on model subsystems defined by the subsystems considered and their partner subsystems. A small and a large basis set are associated with each subsystem. For partner subsystems in a model system, the small basis set is adopted. By introducing a particular decomposition scheme, the intermolecular potential is written as a sum of effective one-body potentials. The binding energy per atom in an infinite crystal of atoms is the negative value of this one-body potential. The one-body potentials for hcp and fcc structures are calculated for the following nearest neighbor distances (d0): 4.6, 5.1, 5.4, 5.435, 5.5, 5.61, and 6.1 a.u. The equilibrium distance is 5.44 a.u. for both structures. The equilibrium dimer distance is 5.61 a.u. For the larger distances, i.e., d0 > 5.4 a.u., the difference of the effective one-body potentials for the two structures is less than 0.2 microE(h). However, the hcp structure has the lowest effective one-body potential for all the distances considered. For the smallest distance the difference in the effective one-body potential is 3.9 microE(h). Hence, for solid helium, i.e., helium under high pressure, the hcp structure is the preferred one. The error in the calculated effective one-body potential for the distance d0 = 5.61 a.u. is of the order of 1 microE(h) (approximately 0.5%).
通过使用一种针对包含小子系统的大型复合物的新的从头计算模型，研究了氦的六方密堆积（hcp）和面心立方（fcc）结构。新模型是在能量增量方案的框架内制定的。在计算系统内和系统间能量时，引入了模型系统。与每个子系统相关联的是一组由邻近标准定义的伙伴子系统。在独立计算系统内和系统间能量时，计算是在由所考虑的子系统及其伙伴子系统定义的模型子系统上进行的。每个子系统都关联有一个小基组和一个大基组。对于模型系统中的伙伴子系统，采用小基组。通过引入一种特定的分解方案，分子间势被写成有效单体势的总和。无限原子晶体中每个原子的结合能是这个单体势的负值。针对以下最近邻距离（d0）计算了hcp和fcc结构的单体势：4.6、5.1、5.4、5.435、5.5、5.61和6.1原子单位。两种结构的平衡距离均为5.44原子单位。平衡二聚体距离为5.61原子单位。对于较大距离，即d0 > 5.4原子单位，两种结构有效单体势的差异小于0.2微hartree（E(h)）。然而，在所考虑的所有距离下，hcp结构具有最低的有效单体势。对于最小距离，有效单体势的差异为3.9微hartree（E(h)）。因此，对于固态氦，即在高压下的氦，hcp结构是更优的结构。对于距离d0 = 5.61原子单位，计算得到的有效单体势的误差约为1微hartree（E(h)）（约0.5%）。
