Jeziorska Małgorzata, Cencek Wojciech, Patkowski Konrad, Jeziorski Bogumił, Szalewicz Krzysztof
Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
J Chem Phys. 2007 Sep 28;127(12):124303. doi: 10.1063/1.2770721.
Symmetry-adapted perturbation theory (SAPT) was applied to the helium dimer for interatomic separations R from 3 to 12 bohrs. The first-order interaction energy and the bulk of the second-order contribution were obtained using Gaussian geminal basis sets and are converged to about 0.1 mK near the minimum and for larger R. The remaining second-order contributions available in the SAPT suite of codes were computed using very large orbital basis sets, up to septuple-zeta quality, augmented by diffuse and midbond functions. The accuracy reached at this level was better than 1 mK in the same region. All the remaining components of the interaction energy were computed using the full configuration interaction method in bases up to sextuple-zeta quality. The latter components, although contributing only 1% near the minimum, have the largest uncertainty of about 10 mK in this region. The total interaction energy at R=5.6 bohrs is -11.000+/-0.011 K. For R< or =6.5 bohrs, the supermolecular (SM) interaction energies computed by us recently turned out to be slightly more accurate. Therefore, we have combined the SM results for R< or =6.5 bohrs with the SAPT results from 7.0 to 12 bohrs to fit analytic functions for the potential and for its error bars. The potential fit uses the best available van der Waals constants C(6) through C(16), including C(11), C(13), and C(15), and is believed to be the best current representation of the Born-Oppenheimer (BO) potential for helium. Using these fits, we found that the BO potential for the helium dimer exhibits the well depth D(e)=11.006+/-0.004 K, the equilibrium distance R(e)=5.608+/-0.012 bohrs, and supports one bound state for (4)He(2) with the dissociation energy D(0)=1.73+/-0.04 mK, and the average interatomic separation R=45.6+/-0.5 A.
对称适配微扰理论（SAPT）被应用于研究氦二聚体，其原子间间距(R)范围为3至12玻尔。使用高斯双原子基组获得了一阶相互作用能和大部分二阶贡献，在最小值附近以及较大(R)值时收敛到约0.1毫开尔文。使用非常大的轨道基组（高达七重(\zeta)质量）计算了SAPT代码套件中可用的其余二阶贡献，并通过弥散函数和键中函数进行增强。在同一区域，此水平达到的精度优于1毫开尔文。使用全组态相互作用方法在高达六重(\zeta)质量的基组中计算了相互作用能的所有其余分量。后一组分虽然在最小值附近仅贡献1%，但在该区域具有约10毫开尔文的最大不确定性。在(R = 5.6)玻尔时的总相互作用能为(-11.000 \pm 0.011)开尔文。对于(R\leq6.5)玻尔，我们最近计算的超分子（SM）相互作用能结果更准确一些。因此，我们将(R\leq6.5)玻尔的SM结果与7.0至12玻尔范围内的SAPT结果相结合，以拟合势能及其误差条的解析函数。势能拟合使用了现有的最佳范德华常数(C(6))至(C(16))，包括(C(11))、(C(13))和(C(15))，并且被认为是当前氦的玻恩 - 奥本海默（BO）势能的最佳表示。使用这些拟合，我们发现氦二聚体的BO势能表现出阱深(D(e)=11.006 \pm 0.004)开尔文，平衡距离(R(e)=5.608 \pm 0.012)玻尔，并支持((^4He)_2)的一个束缚态，其解离能(D(0)=1.73 \pm 0.04)毫开尔文，平均原子间间距(R = 45.6 \pm 0.5)埃。
