scholarly journals Multicomponent equation-of-motion coupled cluster singles and doubles: Theory and calculation of excitation energies for positronium hydride

2019 ◽  
Vol 150 (16) ◽  
pp. 161102 ◽  
Author(s):  
Fabijan Pavošević ◽  
Sharon Hammes-Schiffer
Keyword(s):  
Equation Of Motion ◽  
Coupled Cluster ◽  
Excitation Energies ◽  
Positronium Hydride

Tensor Hypercontraction Equation-of-Motion Second-Order Approximate Coupled Cluster: Electronic Excitation Energies in O(N4) Time

2013 ◽  
Vol 117 (42) ◽  
pp. 12972-12978 ◽  
Author(s):  
Edward G. Hohenstein ◽  
Sara I. L. Kokkila ◽  
Robert M. Parrish ◽  
Todd J. Martínez
Keyword(s):  
Electronic Excitation ◽  
Equation Of Motion ◽  
Second Order ◽  
Coupled Cluster ◽  
Excitation Energies

scholarly journals Partition of electronic excitation energies: the IQA/EOM-CCSD method

2019 ◽  
Vol 21 (25) ◽  
pp. 13428-13439 ◽  
Author(s):  
Alberto Fernández-Alarcón ◽  
José Luis Casals-Sainz ◽  
José Manuel Guevara-Vela ◽  
Aurora Costales ◽  
Evelio Francisco ◽  
...  
Keyword(s):  
Electronic Excitation ◽  
Noncovalent Interactions ◽  
Equation Of Motion ◽  
Electronic Energy ◽  
Molecular Cluster ◽  
Coupled Cluster ◽  
Energy Partition ◽  
Excitation Energies ◽  
Coupled Cluster Theory ◽  
Interacting Quantum Atoms

We put together equation of motion coupled cluster theory and the interacting quantum atoms electronic energy partition to determine how an absorbed photon changes atomic energies as well as covalent and noncovalent interactions within a molecule or molecular cluster.

scholarly journals How to Stay out of Trouble in RIXS Calculations Within Equation-of-Motion Coupled-Cluster Damped Response Theory? Safe Hitchhiking in the Excitation Manifold by Means of Core-Valence Separation

2019 ◽  
Author(s):  
Kaushik Nanda ◽  
Marta L. Vidal ◽  
Rasmus Faber ◽  
Sonia Coriani ◽  
Anna Krylov
Keyword(s):  
Cross Sections ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Response Theory ◽  
Excitation Energies ◽  
X Ray ◽  
X Ray Scattering ◽  
Novel Approach ◽  
Response Equation ◽  
Divergent Behavior

<div>We present a novel approach for computing resonant inelastic X-ray scattering (RIXS) cross sections within the equation-of-motion coupled-cluster (EOM-CC) framework. The approach is based on recasting the sum-over-state expressions for RIXS moments into a compact form by using damped response theory. Damped response formalism allows one to circumvent problems of divergent behavior of the response equation in the resonant regime. However, the convergence of response equations in the X-ray frequency range is often erratic due to the resonant nature of the virtual core-excited states embedded in the valence ionization continuum. We demonstrate that this problematic behavior can be avoided by extending the core-valence separation (CVS) scheme, which decouples the valence-occupied and core-occupied excitation manifolds, into the response domain. The accuracy of the CVS-enabled damped response theory, implemented within the EOM-EE-CCSD (EOM-CC for excitation energies with single and double excitations) framework, is assessed by comparison against damped EOM-EE-CCSD response calculations. The capabilities of the new approach are illustrated by calculations of RIXS cross sections for benzene and benzene radical cation.</div>

The Effect of Polarizable Environment on Two-Photon Absorption Cross Sections Characterized by the Equation-of-Motion Coupled-Cluster Singles and Doubles Method Combined with the Effective Fragment Potential Approach

2018 ◽  
Author(s):  
Kaushik Nanda ◽  
Anna Krylov
Keyword(s):  
Dipole Moment ◽  
Cross Section ◽  
Cross Sections ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Water Molecules ◽  
Excitation Energies ◽  
Effective Fragment Potential ◽  
Two Photon ◽  
Transition Moments

<div>Solvent can significantly affect nonlinear optical properties of solvated chromophores. We report an extension of a hybrid polarizable embedding method incorporating solvent effects in the electronic structure calculations of two-photon absorp-</div><div>tion (2PA) cross sections. The approach uses the equation-of-motion coupled-cluster singles and doubles method for excitation energies (EOM-EE-CCSD) for the quantum region (QM) and the effective fragment potential (EFP) method for the classical region (MM). The impact of the environment on the 2PA cross sections is investigated in microhydrated clusters of para-nitroaniline, thymine, and deprotonated anionic chromophore of photoactive yellow protein (PYPb). The performance of EOM-EE-CCSD/EFP is assessed by comparing the 2PA cross sections against full quantum</div><div>calculations as well as against non-polarizable QM/MM electrostatic embedding approach. The EOM-EE-CCSD/EFP approach reproduces well the main trends in the</div><div>2PA cross sections across different clusters and its performance improves when few water molecules are included in the QM subsystem. For the studied transitions with the strong charge-transfer character, the errors in the 2PA cross sections correlate with the errors in the excitation energies, transition moments, and dipole-moment differences between the initial and final states. Analysis of the 2PA transitions in terms of natural transition orbitals is also reported. The analysis of 2PA transition densities allows us to introduce a rigorous metric for assessing the domain</div><div>of applicability of QM/MM methods for 2PA cross sections calculations. Finally, the calculations of 2PA cross section of PYPb in bulk water are used to assess the convergence of the 2PA cross sections with respect to the number of water molecules included in the QM subsystem. Relative to the small QM (chromophore only) calculations, the inclusion of water molecules from the first solvation shell leads to a</div><div>large change (∼22%) in the calculated 2PA cross section. The convergence of the key properties, such as the excitation energies, transition moments, and dipole-moment</div><div>differences with the size of the QM subsystem, is investigated using configuration interaction singles method.</div>

The Effect of Polarizable Environment on Two-Photon Absorption Cross Sections Characterized by the Equation-of-Motion Coupled-Cluster Singles and Doubles Method Combined with the Effective Fragment Potential Approach

2018 ◽  
Author(s):  
Kaushik Nanda ◽  
Anna Krylov
Keyword(s):  
Dipole Moment ◽  
Cross Section ◽  
Cross Sections ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Water Molecules ◽  
Excitation Energies ◽  
Effective Fragment Potential ◽  
Two Photon ◽  
Transition Moments

<div>Solvent can significantly affect nonlinear optical properties of solvated chromophores. We report an extension of a hybrid polarizable embedding method incorporating solvent effects in the electronic structure calculations of two-photon absorp-</div><div>tion (2PA) cross sections. The approach uses the equation-of-motion coupled-cluster singles and doubles method for excitation energies (EOM-EE-CCSD) for the quantum region (QM) and the effective fragment potential (EFP) method for the classical region (MM). The impact of the environment on the 2PA cross sections is investigated in microhydrated clusters of para-nitroaniline, thymine, and deprotonated anionic chromophore of photoactive yellow protein (PYPb). The performance of EOM-EE-CCSD/EFP is assessed by comparing the 2PA cross sections against full quantum</div><div>calculations as well as against non-polarizable QM/MM electrostatic embedding approach. The EOM-EE-CCSD/EFP approach reproduces well the main trends in the</div><div>2PA cross sections across different clusters and its performance improves when few water molecules are included in the QM subsystem. For the studied transitions with the strong charge-transfer character, the errors in the 2PA cross sections correlate with the errors in the excitation energies, transition moments, and dipole-moment differences between the initial and final states. Analysis of the 2PA transitions in terms of natural transition orbitals is also reported. The analysis of 2PA transition densities allows us to introduce a rigorous metric for assessing the domain</div><div>of applicability of QM/MM methods for 2PA cross sections calculations. Finally, the calculations of 2PA cross section of PYPb in bulk water are used to assess the convergence of the 2PA cross sections with respect to the number of water molecules included in the QM subsystem. Relative to the small QM (chromophore only) calculations, the inclusion of water molecules from the first solvation shell leads to a</div><div>large change (∼22%) in the calculated 2PA cross section. The convergence of the key properties, such as the excitation energies, transition moments, and dipole-moment</div><div>differences with the size of the QM subsystem, is investigated using configuration interaction singles method.</div>

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