Dielectric dependent hybrid functionals

Method developments include deriving and benchmarking hybrid density functionals to compute ground and excited state electronic properties of both condensed and finite systems.

We derived new classes of hybrid functionals with nonempirical parameters that depend on the dielectric screening of the system. These hybrid functionals are referred to as dielectric-dependent hybrid (DDH) functionals.

Screened exchange (SXC) hybrid functional

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Can a unique dielectric constant be defined for molecules or nanocrystals? Dielectric dependent global hybrid functionals (DDH) have remained limited to bulk systems due to this unsolved conceptual problem. We generalized DDH functionals to finite systems by defining an orbital dependent screened exchange (SXC) parameter as a mixing fraction of exact and local exchange. The proposed SXC functional yields accurate fundamental and optical gaps of many, diverse molecular systems in excellent agreement with experiment, including organic and inorganic molecules and semiconducting nanocrystals.

Self-consistent global and range-separated hybrid functionals

We proposed a self-consistent (SC) global hybrid functional and a range separated (RS) one. In the definition of the former, applicable to solids, the dielectric constant of the material (ϵ), computed self-consistently from first principles, is used to determine the global fraction of exact exchange. In the RS version of DDH functionals, applicable to both molecules and solids, the short- and long-range components are matched using system dependent, nonempirical parameters. Both functionals yield accurate electronic properties of inorganic and organic solids, including energy gaps and absolute ionization potentials. The evaluation of SC and RS functionals is computationally less expensive than that of GW self-energies and they can be efficiently utilized to study trends in various properties of solids and molecules; in addition they provide an excellent starting point for G0W0 calculations of specific systems, for example in the case of aqueous solutions. Recently we generalized the SC functionals to interfaces.