Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts

摘要: We compute the absorption and emission energies hence Stokes shifts of small diamondoids as a function size using different theoretical approaches, including density-functional theory (DFT) quantum Monte Carlo (QMC) calculations. The spectra these molecules are also investigated by time-dependent DFT compared with experiment. analyze structural distortion formation self-trapped exciton in excited state, we study effects on shift size. Compared to recent experiments, QMC overestimates excitation about 0.8(1) eV average. Benefiting from cancellation errors, optical gaps obtained calculations B3LYP functional better agreement It is shown that can reproduce most features found experimental spectra. According our calculations, structures state show which hardly noticeable for methane. As number diamond cages increased, mechanism abruptly changes character. have dependent decreases cages. If neglect orbital symmetry excitations, rate decrease is, average, 0.1 per cage diamondoids.