Donor and acceptor levels of organic photovoltaic compounds from first principles

Accurate and efficient approaches to predict the optical properties of organic semiconducting compounds could accelerate the search for efficient organic photovoltaic materials. Nevertheless, predicting the optical properties of organic semiconductors has been plagued by the inaccuracy or computational cost of conventional first-principles calculations. In this work, we demonstrate that orbital-dependent density-functional theory based upon Koopmans' condition [Phys. Rev. B 82, 115121 (2010)] is apt at describing donor and acceptor levels for a wide variety of organic molecules, clusters, and oligomers within a few tenths of an electron-volt relative to experiment, which is comparable to the predictive performance of many-body perturbation theory methods at a fraction of the computational cost.Comment: 13 pages, 11 figure

Koopmans-compliant functionals and their performance against reference molecular data

Koopmans-compliant functionals emerge naturally from extending the constraint of piecewise linearity of the total energy as a function of the number of electrons to each fractional orbital occupation. When applied to approximate density-functional theory, these corrections give rise to orbital-density-dependent functionals and potentials. We show that the simplest implementations of Koopmans' compliance provide accurate estimates for the quasiparticle excitations and leave the total energy functional almost or exactly intact, i.e., they describe correctly electron removals or additions, but do not necessarily alter the electronic charge density distribution within the system. Additional functionals can then be constructed that modify the potential energy surface, including e.g. Perdew-Zunger corrections. These functionals become exactly one-electron self-interaction free and, as all Koopmans-compliant functionals, are approximately many-electron self-interaction free. We discuss in detail these different formulations, and provide extensive benchmarks for the 55 molecules in the reference G2-1 set, using Koopmans-compliant functionals constructed from local-density or generalized-gradient approximations. In all cases we find excellent performance in the electronic properties, comparable or improved with respect to that of many-body perturbation theories, such as G$_0$W$_0$ and self-consistent GW, at a fraction of the cost and in a variational framework that also delivers energy derivatives. Structural properties and atomization energies preserve or slightly improve the accuracy of the underlying density-functional approximations (Note: Supplemental Material is included in the source)

Nowe funkcjonały gęstości elektronowej do modelowania układów związanych niekowalencyjnie

The main part of this work deals with the problem of constructing density-functional methods within the realm of hybrid semilocal approximations, that is, within the set of practical electronic-structure methods that can be applied to real-world molecular systems. In a series of works, the author demonstrates the merits of various building blocks of approximate functionals: the kinetic energy dependence of the exchange-correlation functional, dispersion correction, and long-range correction to the DFT exchange energy. The prototype method which includes these elements is the MCS functional; this method is, however, restricted to the description of noncovalent systems. The final and most complete method devised by the author is a scheme for converting an existing exchange functional into its range-separated hybrid variant. The approach is based on the exchange hole of the Becke-Roussel type, which has the exact second-order expansion in the interelectron distance. The LC-PBETPSS functional, which is constructed by applying this scheme, combines the range-separated PBE exchange lifted to the meta-GGA rung and the TPSS correlation. Numerical tests show remarkably robust performance of the method for noncovalent interaction energies, barrier heights, main-group thermochemistry, and excitation energies