scholarly journals A Comparison of the Interacting Quantum Atoms (IQA) Analysis of the Two-Particle Density-Matrices of MP4SDQ and CCSD

2020 ◽  
Vol 646 (14) ◽  
pp. 1244-1251 ◽  
Author(s):  
Mark A. Vincent ◽  
Arnaldo F. Silva ◽  
Paul L. A. Popelier
Keyword(s):  
Particle Density ◽  
Density Matrices ◽  
Interacting Quantum Atoms

Is it Reasonable to Obtain Information on the Polarizability and Hyperpolarizability Only from the Electron Density?

2018 ◽  
Vol 71 (4) ◽  
pp. 295 ◽  
Author(s):  
Dylan Jayatilaka ◽  
Kunal K. Jha ◽  
Parthapratim Munshi
Keyword(s):  
Density Matrix ◽  
Electron Density ◽  
Ground State ◽  
Density Functional ◽  
Particle Density ◽  
Density Matrices ◽  
Hartree Fock ◽  
Electron Density Matrix ◽  
Ground State Electron ◽  
Side Result

Formulae for the static electronic polarizability and hyperpolarizability are derived in terms of moments of the ground-state electron density matrix by applying the Unsöld approximation and a generalization of the Fermi-Amaldi approximation. The latter formula for the hyperpolarizability appears to be new. The formulae manifestly transform correctly under rotations, and they are observed to be essentially cumulant expressions. Consequently, they are additive over different regions. The properties of the formula are discussed in relation to others that have been proposed in order to clarify inconsistencies. The formulae are then tested against coupled-perturbed Hartree-Fock results for a set of 40 donor-π-acceptor systems. For the polarizability, the correlation is reasonable; therefore, electron density matrix moments from theory or experiment may be used to predict polarizabilities. By constrast, the results for the hyperpolarizabilities are poor, not even within one or two orders of magnitude. The formula for the two- and three-particle density matrices obtained as a side result in this work may be interesting for density functional theories.

Visualizing Covalency and Multiple Bonds in Terms of the Electronic Single-Particle Density Matrix

2001 ◽  
Vol 215 (10) ◽  
Author(s):  
T. Asthalter ◽  
M. Walter
Keyword(s):  
Single Particle ◽  
Organic Molecules ◽  
Graphical Representation ◽  
Particle Density ◽  
Electron System ◽  
Covalent Bonding ◽  
Density Matrices ◽  
Multiple Bonds ◽  
Single Particle Density ◽  
Isoelectronic Series

Two-dimensional cuts through spin-integrated single-particle density matrices (SPDMs) have proven to be a valuable tool to discuss the nature of chemical bonding independent of the degree of rotation of the underlying orbitals in Hilbert space. Starting from a straightforward concept for the interpretation of σ bonds, we briefly present how the transition from purely ionic to mainly covalent bonding is mirrored in the off-diagonal features of the SPDM in the isoelectronic series LiF, BeO and BN. Furthermore, we outline one of several possible ways to extend the graphical representation and interpretation of SPDMs to the case of π bonds in organic molecules and apply it to the conjugated π-electron system 1,6-hexadiynediol.

Equation-of-Motion Coupled-Cluster Method with Double Electron-Attaching Operators: Theory, Implementation, and Benchmarks

2020 ◽  
Author(s):  
Sahil Gulania ◽  
Eirik Fadum Kjønstad ◽  
John F. Stanton ◽  
Henrik Koch ◽  
Anna Krylov
Keyword(s):  
Particle Density ◽  
Equation Of Motion ◽  
Wave Functions ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Bond Breaking ◽  
Coupled Cluster Method ◽  
Density Matrices ◽  
Double Electron ◽  
Structure Patterns

<div> <div> <div> <p>We report a production-level implementation of equation-of-motion coupled-cluster method with double electron- attaching EOM operators of 2p and 3p1h types, EOM-DEA-CCSD. This ansatz, suitable for treating electronic structure patterns that can be described as two-electrons-in-many orbitals, represents a useful addition to EOM-CC family of methods. We analyze the performance of EOM-DEA-CCSD for energy differences and molecular properties. By considering reduced quantities, such as state and transition one-particle density matrices, we can compare EOM-DEA- CCSD wave-functions with wave-functions computed by other EOM-CCSD methods. The benchmarks illustrate that EOM-DEA-CCSD capable of treating diradicals, bond-breaking, and some types of conical intersection. </p> </div> </div> </div>

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