Quantum Monte Carlo, time-dependent density functional theory, and density functional theory calculations of diamondoid excitation energies and Stokes shifts

Abstract

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

29 pages,6 figures,3 tables

References in corpus (9)

• Continuum variational and diffusion quantum Monte Carlo calculations
• Jastrow correlation factor for atoms, molecules, and solids
• Inhomogeneous backflow transformations in quantum Monte Carlo calculations
• Smooth relativistic Hartree-Fock pseudopotentials for H to Ba and Lu to Hg
• Electron Emission from Diamondoids: A Diffusion Quantum Monte Carlo Study
• Norm-conserving Hartree-Fock pseudopotentials and their asymptotic behavior
• Spatially-resolved electronic and vibronic properties of single diamondoid molecules
• Neutral and charged excitations in carbon fullerenes from first-principles many-body theories
• Energies of the first row atoms from quantum Monte Carlo

Cited by in corpus (3)

• Quantum Monte Carlo calculations of energy gaps from first principles
• Diffusion quantum Monte Carlo and GW study of the electronic properties of monolayer and bulk hexagonal boron nitride
• Nodal Variational Principle for Excited States