Spectral properties of molecules and solids from Koopmans-compliant functionals
Nicola Colonna, Paul Scherrer Institut, Switzerland
Accurate first-principles predictions of spectral properties – such as band gaps, band structures, photoemission and absorption spectra – attract considerable attention because of their critical impact on the design and characterization of optical and electronic devices. To date, the most common approaches to compute these quantities are still limited in system size and complexity due to their computational cost an accuracy.
We present a novel functional approach [1,2] that is derived from the density-functional theory by enforcing the correct response to the removal or addition of one electron to the interacting system (Koopmans’s condition). We show that Koopmans-compliant functionals provide a novel framework where spectral properties, and not only total energies, can be efficiently and accurately accounted for.
As an example, ionization potentials of a large set of molecules  (the GW100 test set), photoemission and absorption spectra  of organic donors and acceptors, band gaps and band structures of solids  and liquids  are presented, showing very good agreement with experiment or higher-order theories. Being this a functional framework, the straightforward advantages are that forces and other derivatives are also readily accessible, that the computational costs and complexity are much reduced, and the numerical parameters are those typical of density functional calculations.
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 N. Colonna, N. L. Nguyen, A. Ferretti, and N. Marzari, JCTC 14, 2549 (2018)
 N. Colonna, N. L. Nguyen, A. Ferretti, and N. Marzari, JCTC 15, 1905 (2019)
 J. Elliot, N. Colonna, M. Marsili, N. Marzari and P. Umari, JCTC 15, 3710 (2019)
 N. L. Nguyen, N. Colonna, A. Ferretti, and N. Marzari PRX 8, 021051 (2018)
 J. M. de Almeida, N. L. Nguyen, N. Colonna, W. Chen, C. R. Miranda, A. Pasquarello, and N. Marzari, under review JCTC (2021)