Abinitio study of rotational isomerism in acrolein

1985 ◽  
Vol 63 (7) ◽  
pp. 1672-1680 ◽  
Author(s):  
George R. De Maré
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Dipole Moments ◽  
Relative Energy ◽  
Rotational Isomerism ◽  
Basis Set ◽  
Gradient Force ◽  
Trans Conformation ◽  
Torsional Potential ◽  
Trans Conformer

Analytic gradient (force) methods at the STO-3G, 3-21G, and 6-31G* basis set levels have been used to optimize the geometry of acrolein completely at each critical point (minima, maximum) in the torsional potential energy curves for rotation about the single C—C bond (dihedral angle θ). The STO-3G and 6-31G* optimizations predict the planar trans conformation (θ = 180°) to be more stable than the cis conformation (θ = 0°) by 1.87 and 6.97 kJ/mol, respectively. The 3-21G optimizations, in disagreement with experiment, place the planar cis structure below the trans by 4.5 J/mol. The predicted relative energy (ΔE) and position for the transition state (TS) for rotation from the trans conformer are ΔE = 22.35, 37.14, and 34.41 kJ/mol and θ = 91.8, 91.6, and 91.0° for the STO-3G, 3-21G, and 6-31G* optimizations, respectively. The computed and experimental geometries, relative energies, dipole moments, and coefficients for the torsional potential expansion are compared.

scholarly journals Ab Initioand DFT Studies of Conformational Properties of Heteroatom Containing Ketene Analogues and Their Comparison with the Related Cyclic Analogues

2012 ◽  
Vol 9 (1) ◽  
pp. 193-202 ◽  
Author(s):  
S. Zahra Sayyed-Alangi ◽  
Mohammad T. Baei
Keyword(s):  
Transition State ◽  
Minimum Energy ◽  
Basis Set ◽  
Global Minima ◽  
Stable Conformer ◽  
Trans Conformation ◽  
Conformational Interconversion ◽  
Conformational Properties ◽  
Torsional Angles ◽  
Single Bonds

Minimum-energy and transition state geometries of 3-thioxoprop-2-enethial, 3-thioxoacrylaldehyde, 3-oxoprop-2-enethial, 3-selenoxoprop-2-enethial, 3-thioxoprop-2-eneselenal, 3-selenoxoprop-2-eneselenal, 3-oxoacrylaldehyde, 3-selenoxoacrylaldehyde and 3-oxoprop-2-eneselenal were calculated using HF, B3LYP and MP2 levels of theory and 6-31+G*basis set by rotation around the related -C-C- single bonds. In all of the above mentioned molecules, the s-trans conformation was obtained as the most stable conformer with the 180°dihedral angle, apart from 3-oxoprop-2-enethial and 3-thioxoprop-2-eneselenal which theirs-cisconformers were appeared more stability than related tos-transforms. Their perpendicular geometries, with torsional angles approximately 90°, were as transition state for conformational interconversion between the two global minima forms. Cyclic structures all of the above mentioned molecules were unstable than their linear forms.

Accurate calculations on 20 Λ–S states of the BP radical: potential energy curves, spectroscopic parameters, and electronic transition properties

2015 ◽  
Vol 93 (10) ◽  
pp. 1088-1095 ◽  
Author(s):  
Xinxin Wang ◽  
Deheng Shi ◽  
Jinfeng Sun
Keyword(s):  
Potential Energy ◽  
Dipole Moments ◽  
Potential Energy Curves ◽  
Basis Set ◽  
Weakly Bound ◽  
Transition Dipole ◽  
Spectroscopic Parameters ◽  
Complete Basis Set ◽  
Condon Factors ◽  
S States

The potential energy curves of 20 Λ–S states of BP yeilded from the first two dissociation limits B(2Pu) + P(4Su) and B(2Pu) + P(2Du) have been calculated by the internally contracted multireference configuration interaction approach with the Davidson correction. Especially the core–valence correlation and scalar relativistic corrections are included in the present work. Potential energy curves are also extrapolated to the complete basis set limit. According to the potential energy curves, the spectroscopic parameters are determined and compared with those available in the literature. The convergent behavior of the present calculations is discussed with respect to the basis set and level of theory. Of the 20 states, the 23∑– and 33∑– states have the avoided crossings, which are very weakly bound ones, the 21∑–, and the 13Δ and 23Δ states possess a double well. Subsequently, the transition dipole moments, Franck–Condon factors, and radiative times of the transitions 31Π–b1Π, 23Δ–X3Π, 23∑––A3∑–, 33∑––A3∑–, and 15∑––15Π are calculated.

High level potential energy surface and mechanism of Al(CH3)2OCH3-promoted lactone polymerization: initiation and propagation

2017 ◽  
Vol 19 (13) ◽  
pp. 8989-8999 ◽  
Author(s):  
Stefan Vogt-Geisse ◽  
Ricardo A. Mata ◽  
Alejandro Toro-Labbé
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Stationary State ◽  
Energy Surface ◽  
Relative Energy ◽  
Initiation And Propagation ◽  
Initiation Reaction ◽  
High Level

A hitherto unreported, second transition state (TS2) is the stationary state with the highest relative energy of the Al(CH3)2OCH3 + glycolide initiation reaction.

First-principles computational studies of the torsional potential energy surface of the sec-butyl radical

2011 ◽  
Vol 89 (12) ◽  
pp. 1469-1476 ◽  
Author(s):  
Ya Kun Chen ◽  
Yan Alexander Wang
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
First Principles ◽  
Density Functional ◽  
Energy Surface ◽  
Zero Point ◽  
Basis Set ◽  
Gauche Conformation ◽  
Torsional Potential ◽  
Butyl Radical

First-principles calculations were carried out to investigate the torsional potential energy surface (PES) of the sec-butyl radical. All the wave function methods employed predict a cis-like stable conformation with a dihedral angle of about 47° in addition to the trans-like global minimum conformation and a gauche conformation. However, most of the popular density functional approaches predict only the latter two local minima and lack the cis conformation that was experimentally observed. On the other hand, some density functional methods that incorporate the exact exchange and asymptotically corrected correlation functionals can locate the cis conformation successfully. The basis-set effect was also measured using popular B3LYP and MP2 Hamiltonians: only moderate shape changes were found for PES profiles upon basis-set variations. The stationary structures and their Hessians were obtained at both MP2 and B3LYP levels, with or without incorporating the zero-point energies. Opposite to the relative stability within the Born–Oppenheimer approximation, the cis conformation is more stable than the gauche conformation upon the zero-point correction, consistent with the experiment observations.

Potential energy curves and dipole moment of NF molecule with inner electron correlation

2015 ◽  
Vol 93 (12) ◽  
pp. 1544-1550 ◽  
Author(s):  
Mingjie Wan ◽  
Huafeng Luo ◽  
Chengguo Jin ◽  
Duohui Huang ◽  
Fanhou Wang
Keyword(s):  
Potential Energy ◽  
Excited States ◽  
Correlation Energy ◽  
Dipole Moments ◽  
Electronic States ◽  
Spectroscopic Properties ◽  
Potential Energy Curves ◽  
Basis Set ◽  
Triplet States ◽  
Singlet And Triplet States

The potential energy curves and dipole moments for the low-lying electronic states of the NF molecule are found by using highly accurate multireference configuration interaction plus the Davidson correction with the AV5Z basis set. All 16 electrons are used in the correlation energy calculations, which are used to characterize the spectroscopic properties of a manifold for singlet and triplet states. X3Σ–, a1Δ, b1Σ+, A3Π, 23Σ–, 23Π, 21Δ, 33Σ–, 13Σ+, and 13Δ electronic states correlate with the two lowest dissociation channels N(4Su) + F(2Pu) and N(2Du) + F(2Pu) are investigated. Note that the b1Σ+ state has two depth wells, but only one depth well was observed in the experiment. The spectroscopic parameters (Re, ωe, ωeχe, De, Be, and Te) are derived, which are in excellent agreement with the available experimental data and the other theoretical values. The molecular parameters and dipole moments for the ground and excited states are also obtained.

Active Learning Accelerates Ab Initio Molecular Dynamics on Pericyclic Reactive Energy Surfaces

2020 ◽  
Author(s):  
Shi Jun Ang ◽  
Wujie Wang ◽  
Daniel Schwalbe-Koda ◽  
Simon Axelrod ◽  
Rafael Gomez-Bombarelli
Keyword(s):  
Molecular Dynamics ◽  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Energy Surface ◽  
Computational Cost ◽  
Reactive Trajectories ◽  
Dynamics Simulations ◽  
Energy Surfaces

<div>Modeling dynamical effects in chemical reactions, such as post-transition state bifurcation, requires <i>ab initio</i> molecular dynamics simulations due to the breakdown of simpler static models like transition state theory. However, these simulations tend to be restricted to lower-accuracy electronic structure methods and scarce sampling because of their high computational cost. Here, we report the use of statistical learning to accelerate reactive molecular dynamics simulations by combining high-throughput ab initio calculations, graph-convolution interatomic potentials and active learning. This pipeline was demonstrated on an ambimodal trispericyclic reaction involving 8,8-dicyanoheptafulvene and 6,6-dimethylfulvene. With a dataset size of approximately</div><div>31,000 M062X/def2-SVP quantum mechanical calculations, the computational cost of exploring the reactive potential energy surface was reduced by an order of magnitude. Thousands of virtually costless picosecond-long reactive trajectories suggest that post-transition state bifurcation plays a minor role for the reaction in vacuum. Furthermore, a transfer-learning strategy effectively upgraded the potential energy surface to higher</div><div>levels of theory ((SMD-)M06-2X/def2-TZVPD in vacuum and three other solvents, as well as the more accurate DLPNO-DSD-PBEP86 D3BJ/def2-TZVPD) using about 10% additional calculations for each surface. Since the larger basis set and the dynamic correlation capture intramolecular non-covalent interactions more accurately, they uncover longer lifetimes for the charge-separated intermediate on the more accurate potential energy surfaces. The character of the intermediate switches from entropic to thermodynamic upon including implicit solvation effects, with lifetimes increasing with solvent polarity. Analysis of 2,000 reactive trajectories on the chloroform PES shows a qualitative agreement with the experimentally-reported periselectivity for this reaction. This overall approach is broadly applicable and opens a door to the study of dynamical effects in larger, previously-intractable reactive systems.</div>

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

2020 ◽  
Vol 494 (4) ◽  
pp. 5675-5681 ◽  
Author(s):  
Sanchit Chhabra ◽  
T J Dhilip Kumar
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Cross Sections ◽  
Energy Surface ◽  
Molecular Ions ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

The vibrationally adiabatic torsional potential energy surface of trans-stilbene

2007 ◽  
Vol 440 (1-3) ◽  
pp. 7-11 ◽  
Author(s):  
Praveen D. Chowdary ◽  
Todd J. Martinez ◽  
Martin Gruebele
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Energy Surface ◽  
Torsional Potential ◽  
Trans Stilbene

THE H2NO POTENTIAL ENERGY SURFACE EXPLORED WITH HIGH LEVEL AB INITIO AND DENSITY FUNCTIONAL THEORY METHODS

2007 ◽  
Vol 06 (03) ◽  
pp. 549-562
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Hybrid Methods ◽  
Transition States ◽  
Basis Set ◽  
Functional Theory ◽  
High Level

The transition states for the H 2 NO decomposition and rearrangements mechanisms have been explored by the CBS-Q method or by density functional theory. Six transition states were located on the potential energy surface, which were explored with the Quadratic Complete Basis Set (CBS-Q) and Becke's one-parameter density functional hybrid methods. Interesting deviations between the CBS-Q results and the B1LYP density functional theory lead us to believe that further study into this system is necessary. In the efforts to further assess the stabilities of the transition states, bond order calculations were performed to measure the strength of the bonds in the transition state.

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