A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn–Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation.

A polarizable force-field, based on the Drude oscillator model, has been developed for cholesterol and the sphingomyelin class of lipids crucial to membrane raft formation, with testing performed on several 100 ns simulations. These have been validated against experimental observables as well as previous, nonpolarizable force-fields. Membrane bilayer properties, such as area-per-lipid and membrane thickness, produce results of comparable quantitative accuracy to those from the nonpolarizable force-field, while the membrane dipole potential is computed to be approximately 260 mV for a pure sphingomyelin bilayer, showing quantitative agreement with experimental results.

Absorption and emission spectra arising from the lowest energy transition in BODIPY have been simulated in the gas phase and water using a quantum mechanics/molecular mechanics (QM/MM) approach. Kohn–Sham density functional theory (DFT) is used to calculate both ground (So) and first excited (S1) states using the maximum overlap method to obtain the S1 state. This approach gives ground and excited state structures in good agreement with structures found using multiconfigurational perturbation theory (CASPT2). Application of a post-self-consistent field spin-purification relationship also yields transition energies in agreement with CASPT2 and available experimental data. Spectral bands were simulated using many structures taken from ab initio molecular dynamics simulations of the ground and first excited states. In these simulations, DFT is used for BODIPY, and in the condensed phase simulations the water molecules are treated classically. The resulting spectra show a blue shift of 0.3 eV in both absorption and emission bands in water compared to the gas phase. A Stokes shift of about 0.1 eV is predicted, and the width of the emission band in solution is significantly broader than the absorption band. These results are consistent with experimental data for BODIPY and closely related dyes, and demonstrate how both absorption and emission spectra in solution can be simulated using a quantum mechanical treatment of the electronic structure of the solute.