Tomlinson Aimée, Yaron David
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
J Comput Chem. 2003 Nov 15;24(14):1782-8. doi: 10.1002/jcc.10336.
Intermediate neglect of differential overlap (INDO) is the most commonly utilized semiempirical technique for performing excited state calculations on large organic systems such as organic semiconductors and fluorescent dyes. The calculations are typically done at the singles-configuration interaction (SCI) level. Direct methods provide a more efficient means of performing configuration interaction (CI) calculations, and the computational trade offs associated with various approaches to direct-CI theory have been well characterized for ab initio Hamiltonians and high-order CI. However, the INDO and SCI approximations lead to a new set of trade offs. In particular, application of the electron-electron interactions in the atomic basis leads to savings in computational time that scale as the number of atomic orbitals, which for a large organic system can be two to three orders of magnitude. These savings are largest when only a few low-lying excited states are generated and when a full SCI basis, which includes excitations between all filled and empty molecular orbitals, is used. In addition, substantial memory savings are achieved in the direct method by avoiding the evaluation of the two electron integrals in the molecular orbital basis. The method is demonstrated by calculating the absorption spectrum of a poly(paraphenylenevinylene) oligomer containing 16 phenyl rings.
间略微分重叠（INDO）是用于对诸如有机半导体和荧光染料等大型有机体系进行激发态计算时最常用的半经验技术。这些计算通常在单组态相互作用（SCI）水平上进行。直接方法为进行组态相互作用（CI）计算提供了一种更有效的手段，并且对于从头算哈密顿量和高阶CI，与直接CI理论的各种方法相关的计算权衡已得到充分表征。然而，INDO和SCI近似导致了一组新的权衡。特别是，在原子基中应用电子 - 电子相互作用可节省计算时间，其节省程度与原子轨道数量成比例，对于大型有机体系，这可能相差两到三个数量级。当仅生成少数低激发态且使用包含所有填充和空分子轨道之间激发的完整SCI基时，这些节省最为显著。此外，通过避免在分子轨道基中评估双电子积分，直接方法还能大幅节省内存。通过计算含有16个苯环的聚对苯撑乙烯低聚物的吸收光谱来证明该方法。
