Approaching Phosphorescence Lifetimes in Solution: The Two-Component Polarizable-Embedding Approximate Coupled-Cluster Method

Theoretical description of phosphorescence lifetimes in the condensed phase requires a method that takes into account both spin–orbit coupling and solvent–solute interactions. To obtain such a method, we have coupled our recently developed two-component coupled-cluster method with singles and approximated doubles to a polarizable environment. With this new method, we investigate how different solvents effect the electronic phosphorescence energies and lifetimes of 4<i>H</i>-pyran-4-thione

Analytical Gradients for the MSINDO-sCIS and MSINDO-UCIS Method: Theory, Implementation, Benchmarks, and Examples

Analytical expressions for the sCIS (scaled configuration interaction singles) and UCIS (unrestricted CIS) energy gradients are presented for the semiempirical method MSINDO. The theoretical background of the derivation of the analytical gradients is presented, and the implementation into the MSINDO program package is described. The computational efficiency of the underlying <i>Z</i>-vector method is greatly enhanced by making use of the transpose-free quasiminimal residual (TFQMR) algorithm. Benchmark timing tests are compared to the widely used TD-B3LYP approach. For a statistical evaluation of the accuracy of MSINDO-sCIS, geometry optimizations are performed for a small set of organic molecules in selected excited states. The obtained results are compared to CASPT2 and TD-B3LYP/TZVP. In order to demonstrate the applicability of the present approach to periodic systems within the cyclic cluster model, we present first calculations of the excited state structure of ethyne adsorbed on the NaCl (100) surface