Emil Proynov

Improved meta-GGA Correlation Functional of the Lap Family.

A new correlation functional of the Lap series is derived based on a more elaborated form of correlation wave vectors. Its validation is carried out within two different codes:  deMon-KS3 and Q-Chem 3.0. In deMon the implementation in a post-SCF manner is similar to the preceding BLap3 and Bmτ1 schemes. In Q-Chem the new functional is programmed self-consistently using the integration by parts procedure for the matrix elements. The post-SCF version of the functional deals with three fitting parameters; the previous Lap3 and τ1 functionals have four and five parameters, respectively. The SCF implementation requires only two fitting parameters. Preliminary comparative tests are discussed.

Describing a Strongly Correlated Model System with Density Functional Theory

The linear chain of hydrogen atoms, a basic prototype for the transition from a metal to Mott insulator, is studied with a recent density functional theory model functional for nondynamic and strong correlation. The computed cohesive energy curve for the transition agrees well with accurate literature results. The variation of the electronic structure in this transition is characterized with a density functional descriptor that yields the atomic population of effectively localized electrons. These new methods are also applied to the study of the Peierls dimerization of the stretched even-spaced Mott insulator to a chain of H2 molecules, a different insulator. The transitions among the two insulating states and the metallic state of the hydrogen chain system are depicted in a semiquantitative phase diagram. Overall, we demonstrate the capability of studying strongly correlated materials with a mean-field model at the fundamental level, in contrast to the general pessimistic view on such a feasibility.

Density-functional approach to the three-body dispersion interaction based on the exchange dipole moment.

We implement and compute the density functional nonadditive three-body dispersion interaction using a combination of Tang-Karplus formalism and the exchange-dipole moment model of Becke and Johnson. The computation of the C9 dispersion coefficients is done in a non-empirical fashion. The obtained C9 values of a series of noble atom triplets agree well with highly accurate values in the literature. We also calculate the C9 values for a series of benzene trimers and find a good agreement with high-level ab initio values reported recently in the literature. For the question of damping of the three-body dispersion at short distances, we propose two damping schemes and optimize them based on the benzene trimers data, and the fitted analytic potentials of He3 and Ar3 trimers fitted to the results of high-level wavefunction theories available from the literature. Both damping schemes respond well to the optimization of two parameters.