Patkowski Konrad, Cencek Wojciech, Jeziorska Małgorzata, Jeziorski Bogumił, Szalewicz Krzysztof
Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
J Phys Chem A. 2007 Aug 9;111(31):7611-23. doi: 10.1021/jp071437x. Epub 2007 Jun 6.
Nonrelativistic clamped-nuclei pair interaction energy for ground-state helium atoms has been computed for 12 interatomic separations ranging from 3.0 to 9.0 bohr. The calculations applied the supermolecular approach. The major part of the interaction energy was obtained using the Gaussian geminal implementation of the coupled-cluster theory with double excitations (CCD). Relatively small contributions from single, triple, and quadruple excitations were subsequently included employing the conventional orbital coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and the full configuration interaction (FCI) method. For three distances, the single-excitation contribution was taken from literature Gaussian-geminal calculations at the CCSD level. The orbital CCSD(T) and FCI calculations used very large basis sets, up to doubly augmented septuple- and sextuple-zeta size, respectively, and were followed by extrapolations to the complete basis set limits. The accuracy of the total interaction energies has been estimated to be about 3 mK or 0.03% at the minimum of the potential well. For the attractive part of the well, the relative errors remain consistently smaller than 0.03%. In the repulsive part, the accuracy is even better, except, of course, for the region where the potential goes through zero. For interatomic separations smaller than 4.0 bohr, the relative errors do not exceed 0.01%. Such uncertainties are significantly smaller than the expected values of the relativistic and diagonal Born-Oppenheimer contributions to the potential.
已针对基态氦原子，在3.0至9.0玻尔的12个原子间间距下计算了非相对论性固定核子对相互作用能。计算采用了超分子方法。相互作用能的主要部分是使用含双激发的耦合簇理论的高斯双电子基函数实现（CCD）获得的。随后，采用含单、双和非迭代三激发的常规轨道耦合簇方法[CCSD(T)]和全组态相互作用（FCI）方法，纳入了单、三、四重激发的相对较小贡献。对于三个间距，单激发贡献取自文献中CCSD水平的高斯双电子基函数计算。轨道CCSD(T)和FCI计算分别使用了非常大的基组，最大分别达到双加 Augmented septuple-和sextuple-zeta大小，并随后外推到完全基组极限。据估计，在势阱最小值处，总相互作用能的精度约为3 mK或0.03%。对于势阱的吸引部分，相对误差始终小于0.03%。在排斥部分，精度甚至更好，当然，除了势通过零的区域。对于小于4.0玻尔的原子间间距，相对误差不超过0.01%。这样的不确定性明显小于相对论和对角玻恩-奥本海默对势的贡献的预期值。
