A Configuration Interaction Picture for a Molecular Environment Using Localized Molecular Orbitals: The Excited States of Retinal Proteins

2012 ◽  
Vol 8 (11) ◽  
pp. 4452-4461 ◽  
Author(s):  
Jun-ya Hasegawa ◽  
Kazuhiro J. Fujimoto ◽  
Tsutomu Kawatsu
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Molecular Orbitals ◽  
Interaction Picture ◽  
Localized Molecular Orbitals ◽  
Retinal Proteins

Localized molecular orbitals for excited states of polyenals, polyendials, and polyenones

2003 ◽  
Vol 97 (1) ◽  
pp. 688-699 ◽  
Author(s):  
J. Pitarch-Ruiz ◽  
S. Evangelisti ◽  
D. Maynau
Keyword(s):  
Excited States ◽  
Molecular Orbitals ◽  
Localized Molecular Orbitals

Molecular orbital calculations on dinitrogen trioxide, N2O3

1977 ◽  
Vol 30 (12) ◽  
pp. 2613 ◽  
Author(s):  
IJ Doonan ◽  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Molecular Orbital Calculation ◽  
Molecular Orbitals ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Localized Molecular Orbitals ◽  
Expansion Technique ◽  
Doubly Excited ◽  
Slater Basis

A minimal Slater basis set molecular orbital calculation on dinitrogen trioxide, N2O3, is reported. In the evaluation of integrals, non-NDDO integrals were calculated by the 3G/s expansion technique. Analysis of the wave function obtained shows weak bonding between the nitrosyl and nitro fragments and a very weak attractive interaction between the cis- oxygens. The molecular orbitals for N2O3 were expanded in terms of the NO and NO2 molecular orbitals. A correlation diagram linking the N2O3 orbitals with the NO and NO2 orbitals is presented. The localized molecular orbitals for N2O3 are analysed. A configuration interaction calculation involving the ground state and nine doubly excited state configurations is reported. Two excited states have significant contributions. A comparison is made between the results obtained by using a 3G/S expansion and a calculation using a 2G/S expansion.

scholarly journals Quantum Mechanics / Extremely Localized Molecular Orbital Embedding Strategy for Excited-States. 2. Coupling to the Equation-of-Motion Coupled Cluster Method

2020 ◽  
Author(s):  
Giovanni Macetti ◽  
Alessandro Genoni
Keyword(s):  
Quantum Mechanics ◽  
Molecular Orbital ◽  
Excited States ◽  
Quantum Chemical ◽  
Computational Cost ◽  
Equation Of Motion ◽  
Molecular Orbitals ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Localized Molecular Orbitals

Equation-of-Motion Coupled Cluster with single and double excitations (EOM-CCSD) is currently one of the most accurate quantum chemical methods for the investigation of excited-states, but its non-negligible computational cost unfortunately limits its application to small molecules. To extend its range of applicability, one possibility consists in its coupling with the so-called multi-scale embedding techniques. Along this line, in this work we propose the interface of the EOM-CCSD method with the recently developed quantum mechanics / extremely localized molecular orbital (QM/ELMO) strategy, an approach where the chemically relevant region of the investigated system is treated at fully quantum chemical level (QM region), while the remaining part (namely, the chemical environment) is described through transferred and frozen extremely localized molecular orbitals (ELMO subsystem). In order to determine capabilities and limitations of the novel EOM-CCSD/ELMO approach, some validation tests were properly designed and carried out. They indicated that the new approach is particularly useful and efficient in describing local electronic transitions in relatively large systems, for both covalently and non-covalently bonded QM and ELMO regions. In particular, it has been shown that, including only a limited number of atoms in the chemically active subunit, the ELMO-embedded computations enable the reproduction of excitation energies and oscillator strengths resulting from full EOM-CCSD calculations within the limit of chemical accuracy, but with a significantly reduced computational cost. Furthermore, despite the approximation of an embedding potential given by frozen extremely localized molecular orbitals, it was observed that the new strategy is able to satisfactorily account for the effects of the environment.

Localized molecular orbitals for excited states n→π* (CO) excitation

2003 ◽  
Vol 372 (1-2) ◽  
pp. 22-27 ◽  
Author(s):  
Jose Pitarch-Ruiz ◽  
Stefano Evangelisti ◽  
Daniel Maynau
Keyword(s):  
Excited States ◽  
Molecular Orbitals ◽  
Localized Molecular Orbitals

scholarly journals Quantum Mechanics / Extremely Localized Molecular Orbital Embedding Strategy for Excited-States. 2. Coupling to the Equation-of-Motion Coupled Cluster Method

2020 ◽  
Author(s):  
Giovanni Macetti ◽  
Alessandro Genoni
Keyword(s):  
Quantum Mechanics ◽  
Molecular Orbital ◽  
Excited States ◽  
Quantum Chemical ◽  
Computational Cost ◽  
Equation Of Motion ◽  
Molecular Orbitals ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Localized Molecular Orbitals

Equation-of-Motion Coupled Cluster with single and double excitations (EOM-CCSD) is currently one of the most accurate quantum chemical methods for the investigation of excited-states, but its non-negligible computational cost unfortunately limits its application to small molecules. To extend its range of applicability, one possibility consists in its coupling with the so-called multi-scale embedding techniques. Along this line, in this work we propose the interface of the EOM-CCSD method with the recently developed quantum mechanics / extremely localized molecular orbital (QM/ELMO) strategy, an approach where the chemically relevant region of the investigated system is treated at fully quantum chemical level (QM region), while the remaining part (namely, the chemical environment) is described through transferred and frozen extremely localized molecular orbitals (ELMO subsystem). In order to determine capabilities and limitations of the novel EOM-CCSD/ELMO approach, some validation tests were properly designed and carried out. They indicated that the new approach is particularly useful and efficient in describing local electronic transitions in relatively large systems, for both covalently and non-covalently bonded QM and ELMO regions. In particular, it has been shown that, including only a limited number of atoms in the chemically active subunit, the ELMO-embedded computations enable the reproduction of excitation energies and oscillator strengths resulting from full EOM-CCSD calculations within the limit of chemical accuracy, but with a significantly reduced computational cost. Furthermore, despite the approximation of an embedding potential given by frozen extremely localized molecular orbitals, it was observed that the new strategy is able to satisfactorily account for the effects of the environment.

Simple theoretical models for elimination reactions on polar catalysts; The reactivity of halogeno-, hydroxy-, amino- and mercaptopropane

1982 ◽  
Vol 47 (8) ◽  
pp. 2180-2189 ◽  
Author(s):  
Jiří Sedláček
Keyword(s):  
Theoretical Models ◽  
Molecular Orbitals ◽  
Localized Molecular Orbitals ◽  
Hydroxy Amino ◽  
Elimination Reactions ◽  
Simple Models

CNDO/2 calculations have been made for simple models of the adsorption of (CH3)2CHZ molecules (Z = Cl, OH, NH2, and SH) on the surface of polar catalysts. The results of these calculations and their interpretation by the method of configuration analysis in terms of uniformly localized molecular orbitals made it possible to explain satisfactorily a series of experimental facts. The mechanism and stereoselectivity of the reaction as well as reactivity trends for the series of the molecules studied are discussed.

The Importance of Photodissociative Trichloromethanol for Atmospheric Chemistry

2003 ◽  
Vol 68 (12) ◽  
pp. 2297-2308 ◽  
Author(s):  
Max Mühlhäuser ◽  
Melanie Schnell ◽  
Sigrid D. Peyerimhoff
Keyword(s):  
Energy Range ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Configuration Interaction Calculations

Multireference configuration interaction calculations are carried out for ground and excited states of trichloromethanol to investigate two important photofragmentation processes relevant to atmospheric chemistry. For CCl3OH five low-lying excited states in the energy range between 6.1 and 7.1 eV are found to be highly repulsive for C-Cl elongation leading to Cl2COH (X2A') and Cl (X2P). Photodissociation along C-O cleavage resulting in Cl3C (X2A') and OH (X2Π) has to overcome a barrier of about 0.8 eV (13A'', 11A'') and 1.2 eV (13A') because the low-lying excited states 11A'', 13A' and 13A'' become repulsive only after elongating the C-O bond by about 0.3 Å.

Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules

1980 ◽  
Vol 58 (16) ◽  
pp. 1687-1690 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Excitation Energy ◽  
Explicit Expression ◽  
Excited States ◽  
Configuration Interaction ◽  
Excitation Energies ◽  
Carbon Suboxide ◽  
Numerical Examples ◽  
Energy Correction ◽  
Linear Molecules ◽  
Configuration Interaction Calculations

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.

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