Many-body Green's function GW and Bethe-Salpeter study of the optical excitations in a paradigmatic model dipeptide

Carina Faber (1) , Paul Boulanger (1) , Ivan Duchemin (2) , Claudio Attaccalite (1) , Xavier Blase (1)

1 NEEL - TMC - Théorie de la Matière Condensée
2 LSIM - Laboratory of Atomistic Simulation

We study within the many-body Green's function GW and Bethe-Salpeter formalisms the excitation energies of a paradigmatic model dipeptide, focusing on the four lowest-lying local and charge-transfer excitations. Our GW calculations are performed at the self-consistent level, updating first the quasiparticle energies, and further the single-particle wavefunctions within the static Coulomb-hole plus screened-exchange approximation to the GW self-energy operator. Important level crossings, as compared to the starting Kohn-Sham LDA spectrum, are identified. Our final Bethe-Salpeter singlet excitation energies are found to agree, within 0.07 eV, with CASPT2 reference data, except for one charge-transfer state where the discrepancy can be as large as 0.5 eV. Our results agree best with LC-BLYP and CAM-B3LYP calculations with enhanced long-range exchange, with a 0.1 eV mean absolute error. This has been achieved employing a parameter-free formalism applicable to metallic or insulating extended or finite systems.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Carina Faber, Paul Boulanger, Ivan Duchemin, Claudio Attaccalite, Xavier Blase. Many-body Green's function GW and Bethe-Salpeter study of the optical excitations in a paradigmatic model dipeptide. Journal of Chemical Physics, 2013, 139, pp.194308. ⟨10.1063/1.4830236⟩. ⟨hal-00913648⟩