Multiple complete active space self-consistent field solutions
Multiple complete active space self-consistent field solutions
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DOI：
10.1080/0026897031000109293
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发表时间：
2003-07-10
影响因子：
1.7
通讯作者：
Maynau, D
中科院分区：
文献类型：
--
作者：
Angeli, C;Calzado, CJ;Maynau, D
本文证明了弱相互作用系统基态的CASSCF方程在给定的活性空间中存在多个非等价解。例如，在N个弱相互作用的氢分子的情况下，在CAS（2/2）的情况下至少有N个不同的最小值，涉及同一分子上的一个成键轨道和一个反键轨道。类似的结果对于许多相互作用并不小的系统仍然成立。作为一个例子，乙烯分子的情况下进行了讨论，其中三个CAS（2/2）和六个CAS（4/ 4）的非等效最小值。定域轨道的使用允许人们选择想要收敛到的特定解。这些结果对CASSCF计算的影响是重要的，因为通过选择不同的最小值，可以将CASSCF描述集中在给定的特性上（例如，活动轨道的空间位置）。通过这种方式，可以显著减小活动空间的大小，这在大型系统的情况下尤其重要。
It is proved that the CASSCF equations for the ground state of weakly interacting systems admit many non-equivalent solutions for a given type of active space. For instance, in the case of N weakly interacting hydrogen molecules, there are at least N different minima in the case of a CAS(2/2), involving one bonding and one antibonding orbital on the same molecule. A similar result still holds for many systems for which the interaction is far from small. As an example, the case of the ethylene molecule is discussed, where three CAS(2/2) and six CAS(4/ 4) non-equivalent minima are present. The use of localized orbitals permits one to choose the particular solution one wants to converge to. The implications of these results on CASSCF calculations are significant, since by choosing different minima one can focus the CASSCF description on a given characteristic (e.g., the spatial position) of the active orbitals. In this way, a significant reduction of the active-space size is possible, a fact particularly important in the case of large systems.