Zimmerman Paul M
Department of Chemistry, University of Michigan 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
J Phys Chem A. 2017 Jun 22;121(24):4712-4720. doi: 10.1021/acs.jpca.7b03998. Epub 2017 Jun 8.
The method of increments is herein applied to produce accurate singlet-triplet gaps in a variety of challenging polyatomic systems involving main group elements. This strategy computes incremental Full Configuration Interaction (iFCI) energies for the two spin states in a size-extensive n-body expansion. iFCI avoids exponential costs when n is small and thus is dependent on choice of reference function to maintain good accuracy at polynomial cost. The new algorithm presented in this article therefore employs a high-spin perfect pairing reference to capture the major qualities of the singlet and triplet wave functions at n = 0. Systematic studies will show that singlet-triplet gap predictions approach 1 kcal/mol accuracy at small n (n ≤ 3) compared with available experimental and high-level theoretical values.
本文应用增量法在涉及主族元素的各种具有挑战性的多原子体系中精确计算单重态-三重态能隙。该策略在尺寸可扩展的n体展开中计算两种自旋态的增量完全组态相互作用（iFCI）能量。当n较小时，iFCI避免了指数级成本，因此依赖于参考函数的选择，以多项式成本保持良好的精度。因此，本文提出的新算法采用高自旋完美配对参考，以捕捉n = 0时单重态和三重态波函数的主要性质。系统研究表明，与现有的实验值和高水平理论值相比，在小n（n≤3）时，单重态-三重态能隙预测的精度接近1 kcal/mol。
