scholarly journals PAW-mediated ab initio simulations on linear response phonon dynamics of anisotropic black phosphorous monolayer for thermoelectric applications

2018 ◽  
Vol 20 (41) ◽  
pp. 26688-26695 ◽  
Author(s):  
Sushant Kumar Behera ◽  
Pritam Deb
Keyword(s):  
Perturbation Theory ◽  
Ab Initio ◽  
Computational Efficiency ◽  
Wave Operator ◽  
Linear Response ◽  
First Order ◽  
Ab Initio Simulations ◽  
Phonon Dynamics ◽  
Projector Augmented Wave ◽  
Standard Perturbation Theory

The first-order standard perturbation theory combined with ab initio projector augmented wave operator challenges the realization of the standard Sternheimer equation with linear computational efficiency.

scholarly journals Ab Initio Non-Covalent Crystal Field Theory for Lanthanide Complexes: A Multiconfigurational Non-Orthogonal Group Functions Approach

2020 ◽  
Author(s):  
Alessandro Soncini ◽  
MATTEO PICCARDO
Keyword(s):  
Magnetic Properties ◽  
Perturbation Theory ◽  
Ab Initio ◽  
Crystal Field ◽  
Orthogonal Group ◽  
Lanthanide Complexes ◽  
Field Energy ◽  
First Order ◽  
Group Functions ◽  
Metal Ligand

We present a non-orthogonal fragment ab initio methodology for the calculation of crystal field energy levels and magnetic properties in lanthanide complexes, implementing a systematic description of non-covalent contributions to metal-ligand bonding. The approach has two steps. In the first step, appropriate ab initio wavefunctions for the various ionic fragments (lanthanide ion and coordinating ligands) are separately optimized, accounting for the electrostatic influence of the surrounding environment, within various approximations. In the second and final step, the scalar relativistic (DKH2) electrostatic Hamiltonian of the whole molecule is represented on the basis of the optimized metal-ligand multiconfigurational non-orthogonal group functions (MC-NOGF), and reduced to an effective (2J+1)-dimensional non-orthogonal Configuration Interaction (CI) problem via L{\"o}wdin-partitioning. Within the proposed formalism, the projected Hamiltonian can be implemented to any desired order of perturbation theory in the fragment-localised excitations out of the degenerate space, and its eigenvalues and eigenfunctions are systematic approximations to the crystal field energies and wavefunctions. We present a preliminary implementation of the proposed MC-NOGF method to first-order degenerate perturbation theory within our own ab initio code CERES, and compare its performance both with the simpler non-covalent orthogonal ab initio approach Fragment Ab Initio Model Potential (FAIMP) approximation, and with the full CAHF/CASCI-SO method, accounting for metal-ligand covalency in a mean-field manner. We find that energies and magnetic properties for 44 complexes obtained via an iteratively optimized version of our MC-NOGF first-order non-covalent method, compare remarkably well to the full CAHF/CASCI-SO method including metal-ligand covalency, and are superior to the best purely electrostatic results achieved via an iteratively optimized version of the FAIMP approach.<br>

scholarly journals A New Study to the Schrödinger Equation for Modified Potential V(r)=ar2+br-4+cr-6 in Nonrelativistic Three Dimensional Real Spaces and Phases

2015 ◽  
Vol 61 ◽  
pp. 38-48 ◽  
Author(s):  
Abdelmadjid Maireche
Keyword(s):  
Perturbation Theory ◽  
Schrödinger Equation ◽  
Schrodinger Equation ◽  
Bound States ◽  
Three Dimensional ◽  
Noncommutative Space ◽  
Shift Method ◽  
First Order ◽  
Standard Perturbation Theory

In present work, by applying Boopp’s shift method and standard perturbation theory we have generated exact nonrelativistic bound states solution for a modified potential (see formula in paper) in both three dimensional noncommutative space and phase (NC: 3D-RSP) at first order of two two infinitesimal parameters antisymmetric (see formula in paper), we have also derived the corresponding noncommutative Hamiltonian.

scholarly journals Ab Initio Non-Covalent Crystal Field Theory for Lanthanide Complexes: A Multiconfigurational Non-Orthogonal Group Functions Approach

2020 ◽  
Author(s):  
Alessandro Soncini ◽  
MATTEO PICCARDO
Keyword(s):  
Magnetic Properties ◽  
Perturbation Theory ◽  
Ab Initio ◽  
Crystal Field ◽  
Orthogonal Group ◽  
Lanthanide Complexes ◽  
Field Energy ◽  
First Order ◽  
Group Functions ◽  
Metal Ligand

We present a non-orthogonal fragment ab initio methodology for the calculation of crystal field energy levels and magnetic properties in lanthanide complexes, implementing a systematic description of non-covalent contributions to metal-ligand bonding. The approach has two steps. In the first step, appropriate ab initio wavefunctions for the various ionic fragments (lanthanide ion and coordinating ligands) are separately optimized, accounting for the electrostatic influence of the surrounding environment, within various approximations. In the second and final step, the scalar relativistic (DKH2) electrostatic Hamiltonian of the whole molecule is represented on the basis of the optimized metal-ligand multiconfigurational non-orthogonal group functions (MC-NOGF), and reduced to an effective (2J+1)-dimensional non-orthogonal Configuration Interaction (CI) problem via L{\"o}wdin-partitioning. Within the proposed formalism, the projected Hamiltonian can be implemented to any desired order of perturbation theory in the fragment-localised excitations out of the degenerate space, and its eigenvalues and eigenfunctions are systematic approximations to the crystal field energies and wavefunctions. We present a preliminary implementation of the proposed MC-NOGF method to first-order degenerate perturbation theory within our own ab initio code CERES, and compare its performance both with the simpler non-covalent orthogonal ab initio approach Fragment Ab Initio Model Potential (FAIMP) approximation, and with the full CAHF/CASCI-SO method, accounting for metal-ligand covalency in a mean-field manner. We find that energies and magnetic properties for 44 complexes obtained via an iteratively optimized version of our MC-NOGF first-order non-covalent method, compare remarkably well to the full CAHF/CASCI-SO method including metal-ligand covalency, and are superior to the best purely electrostatic results achieved via an iteratively optimized version of the FAIMP approach.<br>

Quantum Mechanical Interpretation of the Ultra-Low Energy Methyl-Rotation Dynamics in Porous Metal-Organic Frameworks Probed by Low-Frequency Vibrational Spectroscopy and ab initio Simulations

2018 ◽  
Author(s):  
Qi Li ◽  
Adam J. Zaczek ◽  
Timothy M. Korter ◽  
J. Axel Zeitler ◽  
Michael T. Ruggiero
Keyword(s):  
Ab Initio ◽  
Metal Organic Frameworks ◽  
Low Frequency ◽  
Rotor Dynamics ◽  
Quantum Mechanical ◽  
Valuable Insight ◽  
Void Space ◽  
Ab Initio Simulations ◽  
Metal Organic ◽  
Insight Into

<div>Understanding the nature of the interatomic interactions present within the pores of metal-organic frameworks</div><div>is critical in order to design and utilize advanced materials</div><div>with desirable applications. In ZIF-8 and its cobalt analogue</div><div>ZIF-67, the imidazolate methyl-groups, which point directly</div><div>into the void space, have been shown to freely rotate - even</div><div>down to cryogenic temperatures. Using a combination of ex-</div><div>perimental terahertz time-domain spectroscopy, low-frequency</div><div>Raman spectroscopy, and state-of-the-art ab initio simulations,</div><div>the methyl-rotor dynamics in ZIF-8 and ZIF-67 are fully charac-</div><div>terized within the context of a quantum-mechanical hindered-</div><div>rotor model. The results lend insight into the fundamental</div><div>origins of the experimentally observed methyl-rotor dynamics,</div><div>and provide valuable insight into the nature of the weak inter-</div><div>actions present within this important class of materials.</div>

scholarly journals Early-stage formation of (hydr)oxo bridges in transition-metal catalysts for photosynthetic processes

2021 ◽  
Author(s):  
Shin Nakamura ◽  
Matteo Capone ◽  
Giuseppe Mattioli ◽  
Leonardo Guidoni
Keyword(s):  
Transition Metal ◽  
Aqueous Solutions ◽  
Ab Initio ◽  
Early Stage ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Electrochemical Potential ◽  
Ab Initio Simulations

Water-oxidizing metal-(hydr)oxo catalyst films can be generally deposited and activated by applying a positive electrochemical potential to suitable starting aqueous solutions. Here, we used ab initio simulations based on density...

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