Green’s Function Coupled-Cluster Approach: Simulating Photoelectron Spectra for Realistic Molecular Systems

Abstract

In this paper, we present an efficient implementation for the analytical energy-dependent Green's function coupled-cluster with singles and doubles (GFCCSD) approach with our first practice being computing spectral functions of realistic molecular systems. Because of its algebraic structure, the presented method is highly scalable and is capable of computing spectral function for a given molecular system in any energy region. Several typical examples have been given to demonstrate its capability of computing spectral functions not only in the valence band but also in the core-level energy region. Satellite peaks have been observed in the inner valence band and core-level energy region where a many-body effect becomes significant and the single particle picture of ionization often breaks down. The accuracy test has been carried out by extensively comparing the computed spectral functions by our GFCCSD method with experimental photoelectron spectra as well as the theoretical ionization potentials obtained from other methods. It turns out the GFCCSD method is able to provide a qualitative or semiquantitative level of description of ionization processes in both the core and valence regimes. To significantly improve the GFCCSD results for the main ionic states, a larger basis set can usually be employed, whereas the improvement of the GFCCSD results for the satellite states needs higher-order many-body terms to be included in the GFCC implementation.

Coupled Cluster as an Impurity Solver for Green’s Function Embedding Methods

“…The earliest are from Nooijen and coworkers 22,23 while the most recent ones can be found in Ref. 13,[24][25][26]. These solve for the Green's function using linear equations on the real axis.…”

Third-order algebraic diagrammatic construction theory for electron attachment and ionization energies: Conventional and Green’s function implementation

“…[1][2][3][4][5] For molecular systems, a variety of theoretical approaches for computing EA and IP have been developed, ranging from affordable density functional theory (DFT) and time-dependent many-body perturbation theory (MBPT) [6][7][8][9][10][11][12] approximations to highly accurate coupled cluster (CC) methods in their state-specific or equation-of-motion (EOM) formulations. [13][14][15][16][17][18][19][20][21][22][23] Although materials simulations have been traditionally dominated by DFT and MBPT, recent methodological advances and increase in computer power have enabled computations of band structures of three-dimensional semiconductors using equation-of-motion coupled cluster theory (EA/IP-EOM-CC), in a good agreement with experimental results. 20,21 Despite these initial successes, simulations of EA and IP of solids and large molecular systems using accurate ab initio methods such as EOM-CC are far from routine, primarily due to their high computational cost.…”

Coupled Cluster Green's function formulations based on the effective Hamiltonians

“…[35][36][37][38][39][40][41][42][43] The coupled cluster Green's function formulation originally introduced by Nooijen and Snijders in a series of papers published in the early nineties [44][45][46] (see also Ref. [47]) has been recently re-adopted by several groups in studies of atomic/molecular, [48][49][50][51][52][53] and condensed phase and periodic systems, [19,54] where the efficiency of models built upon inclusion hierarchy of collective many-body effect * nicholas.bauman@pnnl.gov † peng398@pnnl.gov ‡ karol.kowalski@pnnl.gov has been examined. Recent progress in CC theory led to the emergence of techniques for downfolding or dimensionality reduction of the electronic Hamiltonians.…”

“…In this paper, we examine a variant of the GFCC formulations that utilize this class of effective Hamiltonians. In particular, our focus is on the active-space GFCC formulations that utilize standard GFCC models that build upon single, double (GFCCSD) [44][45][46]49] and single, double, and internal triple excitations (the so-called GFCC-i(2,3) approximation of Ref. [55]).…”