Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
J Chem Phys. 2013 Aug 14;139(6):064313. doi: 10.1063/1.4817536.
The excitation energies of the four lowest-lying singlet excited states of the TiO2, Ti2O4, and Ti3O6 clusters are calculated by a variety of different Equation-of-Motion Coupled Cluster (EOM-CC) approaches in order to obtain benchmark values for the optical excitations of titanium dioxide clusters. More specifically we investigate what the effect is of the inclusion of triple excitations "triples" in the (EOM-)CC scheme on the calculated excited states of the clusters. While for the monomer and dimer the inclusion of triples is found to only cause a rigid shift in the excitation energies, in the case of the trimer the crossing of the excited states is observed. Coupled cluster approaches where triples are treated perturbatively were found to offer no advantage over EOM-CCSD, whereas the active-space methods (EOM-CCSDt(II/I)) were demonstrated to yield results very close to full EOM-CCSDT, but at a much reduced computational cost.
为了获得二氧化钛团簇的光学激发的基准值，通过各种不同的运动方程耦合簇（EOM-CC）方法计算了 TiO2、Ti2O4 和 Ti3O6 团簇的四个最低单重激发态的激发能。更具体地说，我们研究了在（EOM-）CC 方案中包含三重激发“三重态”对团簇计算激发态的影响。对于单体和二聚体，发现包含三重态只会导致激发能的刚性移动，而在三聚体的情况下，观察到激发态的交叉。发现三重态被微扰处理的耦合簇方法并没有比 EOM-CCSD 更有优势，而活性空间方法（EOM-CCSDt(II/I)）则被证明可以得到非常接近全 EOM-CCSDT 的结果，但计算成本大大降低。
