Charge transfer energies of benzene physisorbed on a graphene sheet from constrained density functional theory

Abstract

Constrained density functional theory (CDFT) is used to evaluate the energy level alignment of a benzene molecule as it approaches a graphene sheet. Within CDFT the problem is conveniently mapped onto evaluating total energy differences between different charge-separated states, and it does not consist in determining a quasiparticle spectrum. We demonstrate that the simple local density approximation provides a good description of the level alignment along the entire binding curve, with excellent agreement to experiments at an infinite separation and to GW calculations close to the bonding distance. The method also allows us to explore the effects due to the presence of graphene structural defects and of multiple molecules. In general, all our results can be reproduced by a classical image charge model taking into account the finite dielectric constant of graphene.

Optimization of constrained density functional theory

“…In practice, cDFT has proven to be a very efficient approach for simulating neutral excitations in molecular systems, particularly in cases where a clear spatial delineation may be made between charge (or spin) donor and acceptor regions 4-7, [17][18][19][21][22][23][24] . cDFT is a significant asset, therefore, to the simulation of exciton formation, where the incorrect long-ranged behaviour of conventional local or semi-local exchange-correlation functionals may be partially corrected by using appropriately con-structed constraints 19,[23][24][25][26] .…”

“…In practice, cDFT has proven to be a very efficient approach for simulating neutral excitations in molecular systems, particularly in cases where a clear spatial delineation may be made between charge (or spin) donor and acceptor regions 4-7, [17][18][19][21][22][23][24] . cDFT is a significant asset, therefore, to the simulation of exciton formation, where the incorrect long-ranged behaviour of conventional local or semi-local exchange-correlation functionals may be partially corrected by using appropriately con-structed constraints 19,[23][24][25][26] . It has also been used to calculate electron transfer 11,[27][28][29][30][31][32][33][34][35][36] , excitation energy transfer 37,38 , and exchange coupling parameters 14,15,39 for use in model Hamiltonians, as well as Coulomb interaction parameters for methods such as DFT+U [40][41][42][43][44][45] .…”

Morphology dependent interaction between Co(ii)-tetraphenylporphyrin and the MgO(100) surface

“…In the case of metals, it is a result of the surface polarization energy and scales with density of states at the Fermi energy 45 , while for semiconductors it is governed by the band gap 93 . The amount of screening can be estimated with the help of the classical image-potential model 94 , through a fit of the exchangecorrelation potential to the classical image plane 52 or even the electronic potential change as a result of the presence of the positively/negatively charged molecule via Wannier functions 53 or constrained DFT 51,96 .…”

Wannier-function-based constrained DFT with nonorthogonality-correcting Pulay forces in application to the reorganization effects in graphene-adsorbed pentacene

“…The present work utilises the same underlying linear-scaling cDFT implementation, itself an extension of a linear-scaling implementation of DFT+U 57 using nonorthogonal generalized Wannier functions. Also relevant to this work is that cDFT has been used to simulate removal or addition of electrons from adsorbed molecule in the context of calculating charge transfer energies 58,59 . Here we use cDFT in conjunction with nonorthogonality Pulay forces to calculate the reorganization energy of a pentacene molecule physisorbed on a flake of graphene.…”