An inequality formulation of conformational energy differences

1976 ◽  
Vol 54 (4) ◽  
pp. 526-530 ◽  
Author(s):  
Johannes Pieter Colpa ◽  
H. Bernhard Schlegel ◽  
Saul Wolfe
Keyword(s):  
Theoretical Analysis ◽  
Transition State ◽  
Geometry Optimization ◽  
Energy Difference ◽  
Basis Set ◽  
Lower State ◽  
Energy Minimum ◽  
Numerical Tests ◽  
Pyramidal Inversion ◽  
True Energy

A theoretical analysis has been performed of the effects of geometry optimization upon computed barriers to rotation and pyramidal inversion. It is shown that, where ΔE is the true energy difference between the energy minimum and the transition state for a particular conformational process, (barrier using the optimized geometry of the lower state) > ΔE > (barrier using the optimized geometry of the higher state). Some numerical tests of this inequality are discussed. These reveal certain limitations upon the assumption that an optimized geometry is transferable from one basis set to another.

Saddle-point geometries and barriers to internal rotation of formamide : an ab initio study

1980 ◽  
Vol 33 (2) ◽  
pp. 249 ◽  
Author(s):  
L Radom ◽  
NV Riggs
Keyword(s):  
Transition State ◽  
Ground State ◽  
Energy Surface ◽  
Saddle Points ◽  
Geometry Optimization ◽  
Internal Motion ◽  
Basis Set ◽  
Minimal Basis ◽  
Experimental Values ◽  
Extended Basis

By use of a direct transition-state program and the STO-3G minimal basis set, two saddle-points are detected on the energy surface for internal motion of formamide. These correspond mainly to rotation about the C-N bond along with some lengthening of this bond and increased pyramidal distortion at nitrogen as compared with that in the ground state. The STO-3G estimates of the barrier height (34-39 kJ mol-1) are in very poor agreement with experimental values (70-90 kJ mol-1), but 4- 31G energy evaluations for the STO-3G-optimized structures give much better estimates (62-80 kJ mol-1). Contrary to a previous report, use of the 4-31G extended basis set for geometry optimization suggests that only the lower-energy member (NH2 cis to CO) of the above pair is a true transition state for internal motion of formamide; its energy relative to that of the 4-31G-optimized ground state (planar) is 83.5 kJ mol-1, very close to the midpoint of the experimental range. The transition state appears to lie in a region of the 4-31G energy surface that is relatively flat with respect to pyramidal distortion at nitrogen; constraining the amino group to planarity raises the calculated energy by only 6.5kJmol-1.

scholarly journals Geometric and energetic data from quantum chemical calculations of halobenzenes and xylenes

2020 ◽  
Author(s):  
Sopanant Datta ◽  
Taweetham Limpanuparb
Keyword(s):  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical Calculation ◽  
Quantum Chemical ◽  
Software Package ◽  
Geometry Optimization ◽  
Theoretical Data ◽  
Basis Set ◽  
Chemical Calculation ◽  
Custom Made

<p>This article presents theoretical data on geometric and energetic features of halobenzenes and xylenes. Data were obtained from <i>ab initio</i> geometry optimization and frequency calculations at HF, B3LYP, MP2 and CCSD levels of theory on 6-311++G(d,p) basis set. In total, 1504 structures of halobenzenes, three structures of xylenes and one structure of benzene were generated and processed by custom-made codes in Mathematica. The quantum chemical calculation was completed in Q-Chem software package. Geometric and energetic data of the compounds are presented in this paper as supplementary tables. Raw output files as well as codes and scripts associated with production and extraction of data are also provided.</p>

scholarly journals Distinctive Supramolecular Features of β-Cyclodextrin Inclusion Complexes with Antidepressants Protriptyline and Maprotiline: A Comprehensive Structural Investigation

2021 ◽  
Vol 14 (8) ◽  
pp. 812
Author(s):  
Thammarat Aree
Keyword(s):  
Inclusion Complexes ◽  
Density Functional ◽  
Water Solubility ◽  
Geometry Optimization ◽  
Binding Constants ◽  
Basis Set ◽  
Full Geometry Optimization ◽  
Basis Set Superposition Error ◽  
X Ray ◽  
Molecular Stability

Depression, a global mental illness, is worsened due to the coronavirus disease 2019 (COVID-2019) pandemic. Tricyclic antidepressants (TCAs) are efficacious for the treatment of depression, even though they have more side effects. Cyclodextrins (CDs) are powerful encapsulating agents for improving molecular stability, water solubility, and lessening the undesired effects of drugs. Because the atomic-level understanding of the β-CD–TCA inclusion complexes remains elusive, we carried out a comprehensive structural study via single-crystal X-ray diffraction and density functional theory (DFT) full-geometry optimization. Here, we focus on two complexes lining on the opposite side of the β-CD–TCA stability spectrum based on binding constants (Kas) in solution, β-CD–protriptyline (PRT) 1—most stable and β-CD–maprotiline (MPL) and 2—least stable. X-ray crystallography unveiled that in the β-CD cavity, the PRT B-ring and MPL A-ring are aligned at a nearly perfect right angle against the O4 plane and primarily maintained in position by intermolecular C–H···π interactions. The increased rigidity of the tricyclic cores is arising from the PRT -CH=CH- bridge widens, and the MPL -CH2–CH2- flexure narrows the butterfly angles, facilitating the deepest and shallower insertions of PRT B-ring (1) and MPL A-ring (2) in the distorted round β-CD cavity for better complexation. This is indicated by the DFT-derived complex stabilization energies (ΔEstbs), although the complex stability orders based on Kas and ΔEstbs are different. The dispersion and the basis set superposition error (BSSE) corrections were considered to improve the DFT results. Plus, the distinctive 3D arrangements of 1 and 2 are discussed. This work provides the first crystallographic evidence of PRT and MPL stabilized in the β-CD cavity, suggesting the potential application of CDs for efficient drug delivery.

A density functional approach toward structural features and properties of C20…N2X2 (X = H, F, Cl, Br, Me) molecules

2014 ◽  
Vol 13 (04) ◽  
pp. 1450023 ◽  
Author(s):  
Reza Ghiasi ◽  
Morteza Zaman Fashami ◽  
Amir Hossein Hakimioun
Keyword(s):  
Density Functional ◽  
Chemical Shifts ◽  
Geometry Optimization ◽  
Structural Features ◽  
Nbo Analysis ◽  
Basis Set ◽  
Basis Sets ◽  
Basis Set Superposition Error ◽  
Homo And Lumo ◽  
Lowest Unoccupied Molecular Orbitals

In this work, the interaction of C 20 with N 2 X 2 ( X = H , F , Cl , Br , Me ) molecules has been explored using the B3LYP, M062x methods and 6-311G(d,p) and 6-311+G(d,p) basis sets. The interaction energies (IEs) obtained with standard method were corrected by basis set superposition error (BSSE) during the geometry optimization for all molecules at the same levels of theory. It was found C 20… N 2 H 2 interaction is stronger than the interaction of other N 2 X 2 ( X = F , Cl , Br , Me ) with C 20. Highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively) levels are illustrated by density of states spectra (DOS). The nucleus-independent chemical shifts (NICSs) confirm that C 20… N 2 X 2 molecules exhibit aromatic characteristics. Geometries obtained from DFT calculations were used to perform NBO analysis. Also, 14 N NQR parameters of the C 20… N 2 X 2 molecules are predicted.

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.

Non-Linear Optical Properties and Global Reactivity Descriptors by ab initio Hartree-Fock (H.F.) Calculations of Simple Coumarins

2021 ◽  
Vol 9 (2) ◽  
pp. 7-20
Author(s):  
P. Sumalatha ◽  
◽  
N. Muralikrishna ◽  
K.V. Padmavathi ◽  
M. Subbarao ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Potential ◽  
Molecular Descriptors ◽  
Resistance To Change ◽  
Energy Difference ◽  
Polarizable Continuum Model ◽  
Basis Set ◽  
Optical Parameters ◽  
Reactivity Descriptors ◽  
Molecular Hyperpolarizability

In this present analysis, the measurement of optimized molecular structure and molecular hyperpolarizability (βtotal) of simple coumarin molecules were investigated using the HF method at 6-311G basis set level Gaussian09W. The measured nonlinear optical parameters (NLO); polarizability (α), the anisotropy of the polarizability (Δα), and first-order molecular hyperpolarizability (βtotal) of the studied coumarins indicate promising optical properties. The energy difference between HOMO and LUMO helped determine the molecular descriptors; global hardness (η), softness (σ) electronegativity (χ) Chemical potential (μ), and electrophilicity index (ω) in gas and different solvents. The molecular hyperpolarizability (βtotal) and descriptors that have been calculated in the solvent medium were taken into consideration through the Polarizable Continuum Model (PCM), This study shows the high static hyperpolarizability exhibited by HNR, FXT, and CNT and offers the potential the materials may have for NLO devices. The molecular descriptors, hardness, and chemical potential values are high for CNT and UCAcompared to other studied coumarins. This suggested that CNT and CA have the most significant chemical potential resistance to change the number of electrons among the other molecules.

Polynomial preserving virtual elements with curved edges

2020 ◽  
Vol 30 (08) ◽  
pp. 1555-1590 ◽  
Author(s):  
L. Beirão da Veiga ◽  
F. Brezzi ◽  
L. D. Marini ◽  
A. Russo
Keyword(s):  
Theoretical Analysis ◽  
Patch Test ◽  
Small Scale ◽  
Intermediate Scale ◽  
Numerical Tests ◽  
Polynomial Preserving ◽  
Virtual Element

In this paper, we tackle the problem of constructing conforming Virtual Element spaces on polygons with curved edges. Unlike previous VEM approaches for curvilinear elements, the present construction ensures that the local VEM spaces contain all the polynomials of a given degree, thus providing the full satisfaction of the patch test. Moreover, unlike standard isoparametric FEM, this approach allows to deal with curved edges at an intermediate scale, between the small scale (treatable by homogenization) and the bigger one (where a finer mesh would make the curve flatter and flatter). The proposed method is supported by theoretical analysis and numerical tests.

Allowed and Forbidden Reaction Paths for the H2 + D2 Exchange Reaction

1975 ◽  
Vol 53 (4) ◽  
pp. 549-555 ◽  
Author(s):  
James S. Wright
Keyword(s):  
Transition Metal ◽  
Transition State ◽  
Exchange Reaction ◽  
Barrier Height ◽  
Dissociation Energy ◽  
Basis Set ◽  
Reaction Paths ◽  
Double Zeta ◽  
Double Zeta Basis

Symmetry arguments and abinitio s.c.f. calculations (double-zeta basis set) are used to show that the exchange reaction H2+ D2 → 2HD could proceed in a concerted fashion through a six-center transition state. The computed barrier height of 90 kcal/mol for this process lies below the experimental dissociation energy of H2 (but above the computed dissociation energy) and also below the energy required for exchange through a four-center transition state. Either the termolecular(2 + 2 + 2 ) or bimolecular(4 + 2 ) cycloadditions are thermally allowed. The presence of a transition metal would allow the reaction to proceed through a four-center geometry, leading to the formation of a possibly stable metal-H4 complex.

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