Potential energy surface for interactions between two hydrogen molecules.
Potential energy surface for interactions between two hydrogen molecules.
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DOI：
10.1063/1.2975220
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发表时间：
2008-09
期刊：
影响因子：
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通讯作者：
K. Patkowski;W. Cencek;P. Jankowski;K. Szalewicz;J. Mehl;G. Garberoglio;A. Harvey
中科院分区：
文献类型：
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作者：
K. Patkowski;W. Cencek;P. Jankowski;K. Szalewicz;J. Mehl;G. Garberoglio;A. Harvey
本文计算了分子内距离固定在最低振转态平均值的两个基态氢分子之间相互作用的非相对论性钳核能量。计算采用了超分子耦合簇方法，单，双和非迭代三重激发[CCSD（T）]和非常大的轨道基础设置，以增加五倍zeta大小补充键函数。相同的基组用于主要针对较大分离进行的微扰理论计算，以提供对超分子方法的独立检查。CCSD（T）以外的贡献计算使用全组态相互作用方法和基组增广的三重zeta加上中键大小。所有计算之后均进行外推，以完成基准设定限值。对于两个代表性点，还使用基数增加1或2的基组进行计算。对于同样的两点，我们还直接用四电子显关联高斯（ECG）函数求解了薛定谔方程。这些额外的计算使我们能够估计用于拟合势的相互作用能的不确定性，在势阱的最小值处约为0.15 K或0.3%。这种精度是一个数量级优于早期的潜力，为这个系统所实现的。对于质心距离R=6.4 bohr的近最小T形构型，ECG计算给出的相互作用能为-56.91+/-0.06 K，而所有点的基组轨道计算给出的相互作用能为-56.96+/-0.16 K。计算点拟合的分析四维势函数。拟合相对于从头算能量的不确定性几乎总是小于后者能量的估计不确定性。对于R=6.34 bohr的T形构型，拟合的全局最小值为-57.12 K。使用路径积分蒙特卡罗方法将拟合应用于计算第二维里系数。所取得的协议与实验是大大优于在任何以前的工作。
Nonrelativistic clamped-nuclei energies of interaction between two ground-state hydrogen molecules with intramolecular distances fixed at their average value in the lowest rovibrational state have been computed. The calculations applied the supermolecular coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and very large orbital basis sets-up to augmented quintuple zeta size supplemented with bond functions. The same basis sets were used in symmetry-adapted perturbation theory calculations performed mainly for larger separations to provide an independent check of the supermolecular approach. The contributions beyond CCSD(T) were computed using the full configuration interaction method and basis sets up to augmented triple zeta plus midbond size. All the calculations were followed by extrapolations to complete basis set limits. For two representative points, calculations were also performed using basis sets with the cardinal number increased by one or two. For the same two points, we have also solved the Schrodinger equation directly using four-electron explicitly correlated Gaussian (ECG) functions. These additional calculations allowed us to estimate the uncertainty in the interaction energies used to fit the potential to be about 0.15 K or 0.3% at the minimum of the potential well. This accuracy is about an order of magnitude better than that achieved by earlier potentials for this system. For a near-minimum T-shaped configuration with the center-of-mass distance R=6.4 bohrs, the ECG calculations give the interaction energy of -56.91+/-0.06 K, whereas the orbital calculations in the basis set used for all the points give -56.96+/-0.16 K. The computed points were fitted by an analytic four-dimensional potential function. The uncertainties in the fit relative to the ab initio energies are almost always smaller than the estimated uncertainty in the latter energies. The global minimum of the fit is -57.12 K for the T-shaped configuration at R=6.34 bohrs. The fit was applied to compute the second virial coefficient using a path-integral Monte Carlo approach. The achieved agreement with experiment is substantially better than in any previous work.