The structures and stabilities of singlet and triplet dithiatriazines: a computational study

1988 ◽  
Vol 66 (9) ◽  
pp. 2279-2284 ◽  
Author(s):  
R. E. Hoffmeyer ◽  
W.-T. Chan ◽  
J. D. Goddard ◽  
R. T. Oakley
Keyword(s):  
Excited States ◽  
Electron Correlation ◽  
Computational Study ◽  
Geometry Optimization ◽  
Hartree Fock ◽  
Structural Distortions ◽  
Energy Gaps ◽  
Jahn Teller ◽  
Moller Plesset ◽  
Triplet Excited States

Ab initio molecular orbital and Møller–Plesset perturbation theory calculations have been carried out on two model dithiatriazines RCN3S2 (R = H, NH2). With geometry optimization and the inclusion of electron correlation both of these dithiatriazines are predicted to be ground state singlets. Both molecules have low-lying triplet excited states, with energy gaps of 6.6 (R = H) and 13.0 (R = NH2) kcal mol−1. The singlet dithiatriazines distort from high (C2v) to low (Cs) symmetry, and these changes are important in determining the relative energies of the singlet and triplet molecules. The structural distortions experienced by these molecules are related to Hartree–Fock and Jahn–Teller instabilities in other thiazene heterocycles.

Excitation Energies from a Partially Spin-Restricted Wave Function

2007 ◽  
Vol 3 (1) ◽  
pp. 65-69 ◽  
Author(s):  
V.N. Glushkov
Keyword(s):  
Wave Function ◽  
Excited States ◽  
Electron Correlation ◽  
Electronic Excitation ◽  
Slater Determinant ◽  
Molecular Orbitals ◽  
Reference Configuration ◽  
Excitation Energies ◽  
Hartree Fock ◽  
Natural Base

A singe Slater determinant consisting of restricted and unrestricted, in spins, parts is proposed to construct a reference configuration for singlet excited states having the same symmetry as the ground one. A partially restricted Hartree-Fock approach is developed to derive amended equations determining the spatial molecular orbitals for singlet excited states. They present the natural base to describe the electron correlation in excited states using the wellestablished spin-annihilated perturbation theories. The efficiency of the proposed method is demonstrated by calculations of electronic excitation energies for the Be atom and LiH molecule.

The 1,2,3,5-ditelluradiazolyl [HCN2Te2] species. Theoretical characterizations of the cation, radical, and radical dimers

1996 ◽  
Vol 74 (6) ◽  
pp. 810-818 ◽  
Author(s):  
William M. Davis ◽  
John D. Goddard
Keyword(s):  
Ab Initio ◽  
Electron Correlation ◽  
Cation Radical ◽  
Building Blocks ◽  
Molecular Conductors ◽  
Face To Face ◽  
Hartree Fock ◽  
Symmetry Constraints ◽  
Moller Plesset ◽  
Low Dimensional

Dithia- and diselena-diazolyl radicals (HCN2E2 E = S, Se) and dimers are important building blocks in the design of low-dimensional molecular conductors. Research on the tellurium-based analogues is much rarer. This work reports the molecular and electronic structures of the cation, radical, and radical dimers of 1,2,3,5-ditelluradiazolyl using ab initio theory including electron correlation by Møller–Plesset perturbation theory up to partial fourth order (MP4SDQ). A face-to-face C2v dimer is predicted to be bound with respect to two radicals by approximately 18 kcal/mol. A C2h, dimer also has been studied and is ca. 2 kcal/mol less stable than the C2v conformer. Relaxing symmetry constraints on the dimers led to more energetically stable structures at the Hartree–Fock level but the C2v structure remains the most stable at a level of theory including electron correlation effects. The results for the Te compounds along with our earlier research on the S and Se analogues provide predictions for the geometries, vibrational frequencies, and ionization potentials for the Te species to assist in future experiments. Key words: tellurium, ab initio, ditelluradiazolyl, dimers, binding.

An approximate ab initio method based on the DIM model

2000 ◽  
Vol 78 (12) ◽  
pp. 1575-1586 ◽  
Author(s):  
John M Cullen
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Basis Sets ◽  
Ab Initio Method ◽  
First Order ◽  
Hartree Fock ◽  
Modified Method ◽  
Electron Correlation Energy

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.

A spectroscopic and computational study of the singlet and triplet excited states of synthetic β-functionalized chlorins

2003 ◽  
Vol 294 (3) ◽  
pp. 285-303 ◽  
Author(s):  
Christian Brückner ◽  
Jason R McCarthy ◽  
Heather W Daniell ◽  
Zeus D Pendon ◽  
Robielyn P Ilagan ◽  
...  
Keyword(s):  
Excited States ◽  
Computational Study ◽  
Triplet Excited States

scholarly journals Calculation of Radial Electron-Electron Distribution function and Expectation Values for Li-Atom in Excited States 1s 2p, 1s 3p and 1s 3d

2015 ◽  
Vol 12 (3) ◽  
pp. 591-596
Author(s):  
Baghdad Science Journal
Keyword(s):  
Distribution Function ◽  
Radial Distribution Function ◽  
Excited States ◽  
Radial Distribution ◽  
Electron Correlation ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
Expectation Values ◽  
Hartree Fock

The electron correlation for inter-shells (1s 2p), (1s 3p) and (1s 3d) was described by the inter-particle radial distribution function f(r12). It was evaluated for Li-atom in the different excited states (1s2 2p), (1s2 3p) and (1s2 3d) using Hartree-Fock approximation (HF). The inter particle expectation values for these shells were also evaluated. The calculations were performed using Mathcad 14 program.

scholarly journals Structure-Reactivity Correlations of Excited States of Perfluorinated Compounds: A Time Resolved Raman Study

1999 ◽  
Vol 19 (1-4) ◽  
pp. 343-348 ◽  
Author(s):  
R. Anandhi ◽  
G. Balakrishnan ◽  
P. Mohandas ◽  
S. Umapathy
Keyword(s):  
Excited States ◽  
Ground State ◽  
Perfluorinated Compounds ◽  
Spectral Studies ◽  
Triplet Excited State ◽  
Time Resolved ◽  
Organic Systems ◽  
Structural Distortions ◽  
Raman Study ◽  
Triplet Excited States

This paper reports the TR3 spectral studies on perfluorinated organic systems with the objective to understand the influence of perfluorination on the excited states. We have recorded the TR3 spectra and Raman excitation profiles of the triplet excited states of decafluorobenzophenone and fluoranil. It is found that the influence of perfluorination is more pronounced in the triplet excited state than the ground state and thus leads to enhanced reactivity for perfluorinated compounds through larger structural distortions.

An Ab Initio Pseudopotential Study of MnPo (M = Cu, Ag, Au; n = 1, 2) Systems

2005 ◽  
Vol 58 (11) ◽  
pp. 792 ◽  
Author(s):  
Qi-Mu Surong ◽  
Yongfang Zhao ◽  
Xiaogong Jing ◽  
Fengli Liu ◽  
Xinying Li ◽  
...  
Keyword(s):  
Bond Length ◽  
Electron Correlation ◽  
Bond Angle ◽  
Relativistic Effects ◽  
Cluster Method ◽  
Coinage Metal ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Moller Plesset ◽  
Correlation Corrections

The small coinage-metal polonium compounds MPo and M2Po, (M = Cu, Ag, Au) are studied at Hartree–Fock (HF), second-order Møller–Plesset perturbation theory (MP2), and coupled cluster method CCSD(T) levels using relativistic and non-relativistic pseudopotentials. The calculated geometries indicate that the M2Po (M = Cu, Ag, Au) systems have bent structures of ~64° angles. Electron correlation corrections to the bond length M–Po are extremely small, but to the bond angle M–Po–M are significant; in general, it was reduced from 86° to 64°. Relativistic effects on bond angle are small, but on bond length are distinct. Both electron correlation effects and relativistic effects are essential to determine the geometry and relative stability of the systems. It can be predicted that Au2Po is relatively stable compared with Ag2Po.

Time-dependent coupled Hartree–Fock calculations of triplet excited states of closed-shell atoms

1985 ◽  
Vol 63 (10) ◽  
pp. 1278-1281 ◽  
Author(s):  
B. Kundu ◽  
P. K. Mukherjee
Keyword(s):  
Excited States ◽  
Excitation Spectrum ◽  
Reasonable Agreement ◽  
Closed Shell ◽  
Time Dependent ◽  
Perturbation Operator ◽  
Hartree Fock ◽  
Effective Form ◽  
Forbidden Transitions ◽  
Triplet Excited States

The nonrelativistic, time-dependent coupled Hartree–Fock theory has been applied to generate the excitation spectrum of two-electron atoms for the forbidden transitions 11S → n3S(n = 2, …, 8), and transition properties are estimated. A simple but effective form of the time-dependent perturbation operator is chosen to get such an excitation spectrum. Reasonable agreement is observed with the available experimental and theoretical estimates.

scholarly journals A General Approach for Multireference Ground and Excited States using Non-Orthogonal Configuration Interaction

2019 ◽  
Author(s):  
Hugh G. A. Burton ◽  
Alex Thom
Keyword(s):  
Excited State ◽  
Excited States ◽  
Configuration Interaction ◽  
System Size ◽  
Model Systems ◽  
Teller Distortion ◽  
Hartree Fock ◽  
Jahn Teller ◽  
Static Correlation ◽  
Small Model

A balanced description of ground and excited states is essential for the description of many chemical processes. However, few methods can handle cases where static correlation is present, and often these scale very unfavourably with system size. Recently, multiple Hartree-Fock (HF) solutions have been proposed as a basis for non-orthogonal configuration interaction (NOCI) to provide multireference ground and excited state energies, although applications across multiple geometries have been limited by the coalescence of HF solutions. Holomorphic HF (h-HF) theory allows solutions to be analytically continued beyond the Coulson-Fischer points at which they vanish but, until now, this has only been demonstrated for small model systems. In this work, we propose a general protocol for computing NOCI ground and excited state energies using multiple HF solutions. To do so, we outline an active space variation of SCF metadynamics that allows a chemically relevant set of HF states to be identified, and describe how these states can be routinely traced across all molecular geometries by exploiting the topology of h-HF solutions in the complex plane. Finally, we illustrate our approach using the dissociation of the fluorine dimer and the pseudo-Jahn-Teller distortion of cyclobutadiene, demonstrating its applicability for multireference ground and excited states. <br>

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