Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), and Donostia International Physics Center, P.K. 1072, 20080 Donostia, Euskadi, Spain.
Phys Chem Chem Phys. 2013 Feb 14;15(6):2055-62. doi: 10.1039/c2cp43559d. Epub 2012 Dec 21.
In this paper, we present for the first time a description based on the natural orbital functional theory (NOFT) of the group VI dimers, namely, Cr(2), Mo(2) and W(2). The PNOF5, Piris Natural Orbital Functional, has been used throughout this work, and the results are compared to multireferential perturbation theory (CASPT2) results. Both methods have been combined with effective core potentials to take into account the scalar relativistic effects. In addition, for Cr(2), an all-electron TZVP quality basis set has also been used to recover the core-valence dynamical correlation. In all cases, PNOF5 shows better behavior than CASPT2, which needs a larger basis set to recover comparable amounts of dynamical correlation. PNOF5 is able to account for the non-dynamical electron correlation, which is responsible for the multireferential nature of these dimers. However, it does not fully recover the dynamical correlation, which is crucial for the accurate description of these challenging potential energy curves. Consequently, PNOF5 predicts longer equilibrium distances and lower dissociation energies than the experimental values. Unlike CASPT2, the PNOF5 results do not significantly improve by using larger basis sets. These new findings represent a major step in the NOFT development, since PNOF5 is the first functional of the natural orbitals reported to yield a chemically balanced and accurate description of these challenging transition metal dimers.
本文首次基于自然轨道函数理论（NOFT）对第六主族的二聚体 Cr(2)、Mo(2) 和 W(2)进行了描述。在整个工作中，我们使用了 PNOF5，即 Piris 自然轨道函数，并将结果与多参考微扰理论（CASPT2）的结果进行了比较。这两种方法都结合了有效核势以考虑标量相对论效应。此外，对于 Cr(2)，我们还使用了全电子 TZVP 质量基组来恢复核价动力学相关。在所有情况下，PNOF5 的表现都优于 CASPT2，后者需要更大的基组才能恢复相当数量的动力学相关。PNOF5 能够解释非动力学电子相关，这是这些二聚体具有多参考性质的原因。然而，它并不能完全恢复动力学相关，这对于准确描述这些具有挑战性的势能曲线至关重要。因此，PNOF5 预测的平衡距离比实验值更长，解离能更低。与 CASPT2 不同，使用更大的基组并不能显著改善 PNOF5 的结果。这些新发现代表了 NOFT 发展的重要一步，因为 PNOF5 是第一个能够对这些具有挑战性的过渡金属二聚体进行化学平衡和准确描述的自然轨道函数。
