Abstract
Five effects of correction of the asymptotic potential error in density functionals are identified that significantly improve calculated properties of molecular excited states involving charge-transfer character. Newly developed materials-science computational methods are used to demonstrate how these effects manifest in materials spectroscopy. Connection is made considering chlorophyll-a as a paradigm for molecular spectroscopy, 22 iconic materials as paradigms for 3D materials spectroscopy, and the VN− defect in hexagonal boron nitride as an example of the spectroscopy of defects in 2D materials pertaining to nanophotonics. Defects can equally be thought of as being “molecular” and “materials” in nature and hence bridge the relms of molecular and materials spectroscopies. It is concluded that the density functional HSE06, currently considered as the standard for accurate calculations of materials spectroscopy, should be replaced, in most instances, by the computationally similar but asymptotically corrected CAM-B3LYP functional, with some specific functionals for materials-use only providing further improvements.
Highlights
The asymptotic potential re ects the energy required to take an electron from a system of interest and remove it to the surrounding vacuum
Developed materials-science computational methods are used to demonstrate how these effects manifest in materials spectroscopy
Connection is made considering chlorophyll-a as a paradigm for molecular spectroscopy, 22 iconic materials as paradigms for 3D materials spectroscopy, and the VNÀ defect in hexagonal boron nitride as an example of the spectroscopy of defects in 2D materials pertaining to nanophotonics
Summary
The asymptotic potential re ects the energy required to take an electron from a system of interest and remove it to the surrounding vacuum. The most commonly used computational method for evaluating spectroscopic properties of molecules and materials, density-functional theory (DFT), can be implemented using functionals embodying many different levels of theory, from the local-density approximation (LDA), to generalised gradient approximations (GGA), to hybrid functionals that mix long-range Hartree–Fock exchange with local exchange, to range-corrected hybrid functionals designed to realistically represent the asymptotic potential, and beyond. This work focuses on the critical effects caused by the difference between basic LDA, GGA, meta-GGA, and hybrid functionals and functions with asymptotic correction: their ability to reliably calculate properties of the excited states of molecules and materials. The critical role of the asymptotic potential was recognised in regard to the evaluation of molecular spectroscopic properties.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] A signi cant bene t from this was a gained ability to simulate excitation energies and exciton couplings in photosynthetic reaction centres.[24,25,26] Even for transitions not involving signi cant electron transfer, the asymptotic potential error can induce large errors in properties such as calculated reorganization energies and their partitioning into the Huang–Rhys factors (electron-vibration coupling constants) that control spectral bandshapes as well as photochemical and photophysical reaction rates.[27,28,29] This occurs as such properties are controlled by the details of the entire excited-state manifold, not just the excited state of primary interest
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