Accurate calculation of Franck-Condon factors for molecules with strongly anharmonic potentials

基于正坐标的振动跃迁的精确计算目前仅限于具有3或4个原子的分子。其原因是非常苛刻的确定可靠的多维势能面，相应的相关振动波函数和frank - condon （FC）因子本身。后一个方面是本建议的主要主题，但也包括基于显式相关耦合簇方法的精确势能面计算。重点是有10或12个原子的分子，它们表现出强烈的非调和势能面。一个例子包括具有双阱势的分子，这可能引起隧道分裂。非谐波振动波函数应通过VSCF/VCI计算（或其修改）确定。分子的大小以及它们强烈的非和谐性需要许多新方法，这是本提案的主题。这包括在VSCF和VCI水平上的FC积分的有效评估，非常快速的振动相关方法的发展和新的非谐波函数预筛选技术。新开发的全自动程序应使用用于系统基准计算，也用于当前感兴趣的分子和分子簇。

The accurate calculation of vibronic transitions based on normal coordinates is currently limited to molecules with 3 or 4 atoms. The reason for this is the very demanding determination of reliable multi-dimensional potential energy surfaces, the corresponding correlated vibrational wave functions and theFranck-Condon (FC) factors themselves. The latter aspect is the primary subject of this proposal, but includes also the calculation of accurate potential energy surfaces based on explicitly correlated coupled-cluster methods. The focus is on molecules with up to 10 or 12 atoms, which show strongly anharmonic potential energy surfaces. An example comprises molecules with double well potentials, which may give rise to tunneling splittings. Anharmonic vibrational wave functions shall be determined by VSCF/VCI calculations (or modifications thereof). The size of the molecules as well as their strong anharmonicities require a number of new methods, which are subject of this proposal. This includes the efficient evaluation of FC integrals at the VSCF and VCI levels, the development of very fast vibration correlation methods and new prescreening techniques for anharmonic wave functions. The newly developed, fully automated program shall be used for systematic benchmark calculations, but also for molecules and molecular clusters of current interest.