Mentel Ł M, Baerends E J
Faculty of Exact Sciences, Theoretical Chemistry, Vrije Universiteit Amsterdam , Amsterdam 1081 HV, The Netherlands.
WCU program, Department of Chemistry, Pohang University of Science and Technology , Pohang, Gyeongsang 790-784, South Korea.
J Chem Theory Comput. 2014 Jan 14;10(1):252-67. doi: 10.1021/ct400990u. Epub 2013 Dec 31.
The basis set superposition effect (BSSE) is a simple concept, and its validity is almost universally accepted. So is the counterpoise method to correct for it. The idea is that the basis set is biased toward the dimer because each monomer in the dimer can "use" the basis functions on the other monomer, which it cannot in a simple monomer calculation. This hypothesis can only be tested if basis set free benchmark numbers are available for monomers and dimer. We are testing the hypothesis on a few systems (in this paper Be2) that are small enough that sufficiently accurate benchmark numbers (basis set free, or close to basis set limit; full CI or close to full CI) are available or can be obtained. We find that the answer to the title question is negative: the standard basis sets of quantum chemistry appear to be biased toward the atom in the sense that basis set errors are larger for the dimer than the monomer. Applying the counterpoise correction increases the imbalance by reducing the already smaller basis set error of the monomer even further. Counterpoise corrected bond energies then deviate more from the basis set limit numbers than uncorrected bond energies. These conclusions hold both at the Hartree-Fock level and (much stronger) at the correlated (CCSD(T), full CI) levels. So the answer to the title question is No.
基组叠加效应(BSSE)是一个简单的概念,其有效性几乎被普遍接受。用于校正该效应的对称操作法也是如此。其观点是,基组会偏向二聚体,因为二聚体中的每个单体都可以“使用”另一个单体上的基函数,而在简单的单体计算中它无法这样做。只有当单体和二聚体有不含基组的基准数值时,才能检验这个假设。我们正在几个体系(本文中的Be2)上检验这个假设,这些体系足够小,以至于可以得到或能够获得足够精确的基准数值(不含基组,或接近基组极限;完全CI或接近完全CI)。我们发现标题问题的答案是否定的:量子化学的标准基组似乎偏向原子,因为二聚体的基组误差比单体的更大。应用对称操作校正会进一步减小已经较小的单体基组误差,从而增加不平衡。经过对称操作校正的键能随后比未校正的键能更偏离基组极限数值。这些结论在哈特里 - 福克水平以及(更显著地)在相关(CCSD(T),完全CI)水平上都成立。所以标题问题的答案是“否”。