scholarly journals Excited-state electronic structure of molecules using many-body Green’s functions: Quasiparticles and electron–hole excitations with VOTCA-XTP

2020 ◽  
Vol 152 (11) ◽  
pp. 114103 ◽  
Author(s):  
G. Tirimbò ◽  
V. Sundaram ◽  
O. Çaylak ◽  
W. Scharpach ◽  
J. Sijen ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Green's Functions ◽  
Green’S Functions ◽  
Many Body ◽  
Electron Hole ◽  
Structure Of Molecules

scholarly journals Excited-State Electronic Structure of Molecules Using Many-Body Green's Functions: Quasiparticles and Electron-Hole Excitations with VOTCA-XTP

2019 ◽  
Author(s):  
Gianluca Tirimbò ◽  
Vivek Sundaram ◽  
Onur Çaylak ◽  
Wouter Scharpach ◽  
Javier Sijen ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Excited States ◽  
Green's Functions ◽  
Green’S Functions ◽  
Molecular Architecture ◽  
Many Body ◽  
Electron Hole ◽  
Structure Of Molecules ◽  
Dynamics Simulations

<div>We present the open-source VOTCA-XTP software for the calculation of the excited-state electronic structure of molecules using many-body Green’s functions theory in the GW approximation with the Bethe–Salpeter Equation (BSE). This work provides a summary of the underlying theory and discusses details of its implementation based on Gaussian orbitals, including, i.a., resolution-of-identity techniques, different approaches to the frequency integration of the self-energy or acceleration by offloading compute-intensive matrix operations using GPUs in a hybrid OpenMP/Cuda scheme. A distinctive feature of VOTCA-XTP is the capability to couple the calculation of electronic excitations to a classical polarizable environment on atomistic level in a coupled quantum- and molecular-mechanics (QM/MM) scheme, where a complex morphology can be imported from Molecular Dynamics simulations. The capabilities and limitations of the GW -BSE implementation are illustrated with two examples. First, we study the dependence of optically active electron-hole excitations in a series of diketopyrrolopyrrole-based oligomers on molecular-architecture modifications and the number of repeat units. Second, we use the GW -BSE/MM setup to investigate the effect of polarization on localized and intermolecular charge-transfer excited states in morphologies of low-donor content rubrene-fullerene mixtures. These showcases demonstrate that our implementation currently allows to treat systems with up to 2500 basis functions on regular shared-memory workstations, providing accurate descriptions of quasiparticle and coupled electron-hole excited states of various character on an equal footing.</div>

scholarly journals Excited-State Electronic Structure of Molecules Using Many-Body Green's Functions: Quasiparticles and Electron-Hole Excitations with VOTCA-XTP

2019 ◽  
Author(s):  
Gianluca Tirimbò ◽  
Vivek Sundaram ◽  
Onur Çaylak ◽  
Wouter Scharpach ◽  
Javier Sijen ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Excited States ◽  
Green's Functions ◽  
Green’S Functions ◽  
Molecular Architecture ◽  
Many Body ◽  
Electron Hole ◽  
Structure Of Molecules ◽  
Dynamics Simulations

<div>We present the open-source VOTCA-XTP software for the calculation of the excited-state electronic structure of molecules using many-body Green’s functions theory in the GW approximation with the Bethe–Salpeter Equation (BSE). This work provides a summary of the underlying theory and discusses details of its implementation based on Gaussian orbitals, including, i.a., resolution-of-identity techniques, different approaches to the frequency integration of the self-energy or acceleration by offloading compute-intensive matrix operations using GPUs in a hybrid OpenMP/Cuda scheme. A distinctive feature of VOTCA-XTP is the capability to couple the calculation of electronic excitations to a classical polarizable environment on atomistic level in a coupled quantum- and molecular-mechanics (QM/MM) scheme, where a complex morphology can be imported from Molecular Dynamics simulations. The capabilities and limitations of the GW -BSE implementation are illustrated with two examples. First, we study the dependence of optically active electron-hole excitations in a series of diketopyrrolopyrrole-based oligomers on molecular-architecture modifications and the number of repeat units. Second, we use the GW -BSE/MM setup to investigate the effect of polarization on localized and intermolecular charge-transfer excited states in morphologies of low-donor content rubrene-fullerene mixtures. These showcases demonstrate that our implementation currently allows to treat systems with up to 2500 basis functions on regular shared-memory workstations, providing accurate descriptions of quasiparticle and coupled electron-hole excited states of various character on an equal footing.</div>

AN INTRODUCTORY GUIDE TO GREEN’S FUNCTION METHODS IN NUCLEAR MANY-BODY PROBLEMS

1994 ◽  
Vol 03 (02) ◽  
pp. 523-589 ◽  
Author(s):  
T.T.S. KUO ◽  
YIHARN TZENG
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Green's Functions ◽  
Green’S Functions ◽  
Model Space ◽  
Many Body ◽  
Diagram Expansion ◽  
Nucleus Scattering ◽  
Many Body Systems ◽  
General Method

We present an elementary and fairly detailed review of several Green’s function methods for treating nuclear and other many-body systems. We first treat the single-particle Green’s function, by way of which some details concerning linked diagram expansion, rules for evaluating Green’s function diagrams and solution of the Dyson’s integral equation for Green’s function are exhibited. The particle-particle hole-hole (pphh) Green’s function is then considered, and a specific time-blocking technique is discussed. This technique enables us to have a one-frequency Dyson’s equation for the pphh and similarly for other Green’s functions, thus considerably facilitating their calculation. A third type of Green’s function considered is the particle-hole Green’s function. RPA and high order RPA are treated, along with examples for setting up particle-hole RPA equations. A general method for deriving a model-space Dyson’s equation for Green’s functions is discussed. We also discuss a method for determining the normalization of Green’s function transition amplitudes based on its vertex function. Some applications of Green’s function methods to nuclear structure and recent deep inelastic lepton-nucleus scattering are addressed.

scholarly journals Exceptional band touching for strongly correlated systems in equilibrium

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Tsuneya Yoshida ◽  
Robert Peters ◽  
Norio Kawakami ◽  
Yasuhiro Hatsugai
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Strongly Correlated Systems ◽  
Strongly Correlated ◽  
Many Body ◽  
Band Structures ◽  
Correlated Systems ◽  
Concise Review ◽  
Open Questions ◽  
Many Body Systems

Abstract Quasi-particles described by Green‘s functions of equilibrium systems exhibit non-Hermitian topological phenomena because of their finite lifetime. This non-Hermitian perspective on equilibrium systems provides new insights into correlated systems and attracts much interest because of its potential to solve open questions in correlated compounds. We provide a concise review of the non-Hermitian topological band structures for quantum many-body systems in equilibrium, as well as their classification.

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