THEORETICAL STUDY OF GLYCINE CONFORMERS

2008 ◽  
Vol 07 (04) ◽  
pp. 889-909 ◽  
Author(s):  
HONG-WEI KE ◽  
LI RAO ◽  
XIN XU ◽  
YI-JING YAN
Keyword(s):  
Potential Energy Surfaces ◽  
Density Functional ◽  
Polarizable Continuum Model ◽  
Basis Sets ◽  
Dft Methods ◽  
Solvent Interactions ◽  
Solvation Effects ◽  
Moller Plesset ◽  
Energy Surfaces ◽  
Polarizable Continuum

Glycine conformers were investigated with three density functional theory (DFT) methods (B3LYP, PBE1PBE, X3LYP), and the second order Møller–Plesset perturbation theory (MP2) combined with basis sets of 6-31+G*, aug-cc-pVDZ, and aug-cc-pVTZ. Solvation effects were considered by using polarizable continuum model. Results from B3LYP and X3LYP were in generally good agreement with those of MP2, while PBE1PBE was shown to be inferior for the description of conformational potential energy surfaces. Conformers Ip, IIp, IIn, IIIp, IIIn, and IVn were all found to be low-lying states within 2.0 kcal/mol, with Ip being the global minimum in gas phase. Solvation effects can significantly change the nature of the conformational surfaces of glycine. A proper description of conformational equilibrium demands for a good treatment of both long-range and short-range solute–solvent interactions.

A Density Functional Theory Study of the Cu+ · O2 and Cu+ · N2 Adducts

2012 ◽  
Vol 67 (2) ◽  
pp. 118-126 ◽  
Author(s):  
Jamal N. Dawoud ◽  
Ismail I. Fasfous ◽  
Amin F. Majdalawieh
Keyword(s):  
Density Functional Theory ◽  
Binding Energy ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Theoretical Data ◽  
Basis Sets ◽  
Dft Methods ◽  
Functional Theory ◽  
Linear Configuration ◽  
Energy Surfaces

The geometries and harmonic vibration frequencies of the Cu+ ·O2 and Cu+ ·N2 are determined by various density functional theory (DFT) methods employing different basis sets. The potential energy surfaces (PES) are examined. The Cu+ ·O2 adduct exhibits a bent structure with a binding energy of 12.4 kcal mol−1, whereas Cu+ ·N2 exhibits a linear configuration with a binding energy of 23.5 kcal mol−1. The binding energy values for the two adducts agree well with the available published experimental and theoretical data and hence are reliable.

Theoretical Investigation of the Decarbonylation of Acetaldehyde by Ni+2 Using Density Functional Theory

2013 ◽  
Vol 446-447 ◽  
pp. 168-171
Author(s):  
Hong Fei Liu ◽  
Xin Min Min ◽  
Hai Xia Yang
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Transition Metal Ions ◽  
Basis Sets ◽  
Functional Theory ◽  
Representative System ◽  
Energy Surfaces ◽  
Ground Potential

The decarbonylation of acetaldehyde assisted by Ni+2, which was selected as a representative system of transition metal ions assisted decarbonylation of acetaldehyde, has been investigated using density functional theory (B3LYP) in conjunction with the 6-31+G** basis sets in C,H,O atoms and Lanl2dz basis sets in Ni atom The geometries and energies of the reactants, intermediates, products and transition states relevant to the reaction were located on the triplet ground potential energy surfaces of [Ni, O, C2,H4]+2. Our calculations indicate the decarbonylation of acetaldehyde takes place through four steps, that is, encounter complexation, CC activation, aldehyde H-shift and nonreactive dissociation, it is that CC activation by Ni+2that lead to the decarbonylation of acetaldehyde.

Jones and magnetoelectric birefringence of pure substances — A computational study

2009 ◽  
Vol 87 (10) ◽  
pp. 1352-1361 ◽  
Author(s):  
Antonio Rizzo ◽  
Dmitry Shcherbin ◽  
Kenneth Ruud
Keyword(s):  
Condensed Phase ◽  
Continuum Model ◽  
Density Functional ◽  
Computational Study ◽  
Polarizable Continuum Model ◽  
Solvent Interactions ◽  
Dipolar Molecules ◽  
Upper Limits ◽  
Order Of Magnitude ◽  
Polarizable Continuum

We present the first investigation of condensed-phase effects on the Jones (and magnetoelectric) birefringence of a set of nondipolar (CCl4 and CS2) and dipolar (nitro- and chloro-benzene) molecules using a recent implementation of the polarizable continuum model for cubic response functions at the time-dependent density-functional level of theory. The condensed-phase calculations have been performed on the neat liquids of the sample molecules using a nonequilibrium solvation scheme to properly account for the solute–solvent interactions in the presence of a frequency-dependent electromagnetic field. It is demonstrated that the condensed-phase effects as modelled by the polarizable continuum model can be substantial, increasing the observable birefringence by more than sixty percent in the case of CCl4, and by a factor of more than three for CS2. Solvent effects are also substantial for the dipolar molecules, leading to an enhancement by a factor of roughly five for nitrobenzene and by a bit less than 30% for chlorobenzene. Comparison is made with the results of experiment. Our calculated anisotropies confirm that the effect is below current experimental detection limits for CCl4 and CS2. We compute Jones constants of the same order of magnitude as the upper limits given in experiment for nitro- and chlorobenzene.

2-Chloro-2,2-difluoracetamide (ClF2CC(O)NH2). Thermal Decomposition, Vapour Infrared, Mass Spectrometry, Low-temperature NMR, and Theoretical Studies. Solvent Effects on Conformational Preferences

2011 ◽  
Vol 64 (10) ◽  
pp. 1366 ◽  
Author(s):  
Ana G. Iriarte ◽  
Edgardo H. Cutin ◽  
Gustavo A. Argüello
Keyword(s):  
Mass Spectrometry ◽  
Thermal Decomposition ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Vapour Phase ◽  
Basis Sets ◽  
Conformational Preferences ◽  
Ft Ir ◽  
Energy Surfaces

Gas-phase thermal decomposition of 2-chloro-2,2-difluoracetamide (CDFA) was studied at temperatures between 270 and 290°C. The rate constant for the decomposition follows the Arrhenius equation. Mass spectrometry was used to analyze the decomposition pattern of the title compound. The FT-IR spectrum of the vapour phase and the infrared spectra of CDFA in protic and aprotic solvents were recorded. Potential energy surfaces were studied by theoretical calculations performed at the density functional theory level (PBEPBE and B3LYP methods) using the 6-31G*, 6-31+G*, 6-311+G**, aug-cc-pVDZ, and aug-cc-pVTZ basis sets.

scholarly journals Calculations of optical rotation: Influence of molecular structure

2012 ◽  
Vol 77 (7) ◽  
pp. 887-898
Author(s):  
Jia Yu ◽  
Yu Cao ◽  
Hang Song ◽  
Xianlong Wang ◽  
Shun Yao
Keyword(s):  
Molecular Structure ◽  
Nitrogen Atom ◽  
Density Functional ◽  
Optical Rotation ◽  
Cyclic Compound ◽  
Polarizable Continuum Model ◽  
Basis Sets ◽  
Dft Methods ◽  
Hartree Fock ◽  
Chiral Compounds

Ab initio Hartree-Fock (HF) method and Density Functional Theory (DFT) were used to calculate the optical rotation of 26 chiral compounds. The effects of theory and basis sets used for calculation, solvents influence on the geometry and values of calculated optical rotation were all discussed. The polarizable continuum model, included in the calculation, did not improve the accuracy effectively, but it was superior to ?s. Optical rotation of five or sixmembered of cyclic compound has been calculated and 17 pyrrolidine or piperidine derivatives which were calculated by HF and DFT methods gave acceptable predictions. The nitrogen atom affects the calculation results dramatically, and it is necessary in the molecular structure in order to get an accurate computation result. Namely, when the nitrogen atom was substituted by oxygen atom in the ring, the calculation result deteriorated.

THEORETICAL STUDY ON THE H2 ACTIVATION BY PtO+ AND ${\rm PtO}_{2}^{+}$ IN THE GAS PHASE

2010 ◽  
Vol 09 (06) ◽  
pp. 963-974 ◽  
Author(s):  
YONGCHUN TONG ◽  
QINGYUN WANG ◽  
DONGQING WU ◽  
YONGCHENG WANG
Keyword(s):  
Potential Energy ◽  
Gas Phase ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Reaction Pathway ◽  
Minimum Energy ◽  
Basis Sets ◽  
Avoided Crossing ◽  
Pass Through ◽  
Energy Surfaces

Gas-phase H2 activation by PtO+ and [Formula: see text] were studied at the density functional level of theory (DFT) using the relativistic effective core potential (RECP) of Stuttgart basis sets on platinum atom and UB3LYP/6-311+G(2d,2p) level on hydrogen and oxygen atoms. Two reaction profiles corresponding to the doublet and quartet multiplicities were investigated in order to ascertain the presence of some spin inversion during the H2 reduction. The electron-transfer reactivity of the reactions were analyzed using the two-state model, and the strongly crossing behavior on the transition state (TS) area were shown. Finally, the actions of frontier molecular orbitals in minimum-energy crossing point (MECP) have been illuminated briefly. These theoretical results can act as a guide to further theoretical and experimental research. H2 activation mediated by metal oxide cations were found to be an exothermic spin-forbidden process resulting from a crossing between quartet and doublet profiles. To evaluate the spin-forbidden process in the reaction pathway, the spin-obit coupling (SOC) matrix elements are calculated at the MECP with the different potential energy surfaces (PESs) and the probability of crossing between the adiabatic potential-energy surfaces during a single pass through the avoided crossing region was described. Therefore, the intersystem crossing (ISC) at crossing points (CP) occur efficiently because of the large SOC (ca. 85.58 cm-1) involved.

scholarly journals Predicting the UV–vis spectra of oxazine dyes

2011 ◽  
Vol 7 ◽  
pp. 432-441 ◽  
Author(s):  
Scott Fleming ◽  
Andrew Mills ◽  
Tell Tuttle
Keyword(s):  
Excitation Energy ◽  
Density Functional ◽  
Polarizable Continuum Model ◽  
Implicit Solvent ◽  
Continuum Approach ◽  
Excitation Energies ◽  
Functional Theory ◽  
Partial Charges ◽  
Td Dft ◽  
Polarizable Continuum

In the current work we have investigated the ability of time-dependent density functional theory (TD-DFT) to predict the absorption spectra of a series of oxazine dyes and the effect of solvent on the accuracy of these predictions. Based on the results of this study, it is clear that for the series of oxazine dyes an accurate prediction of the excitation energy requires the inclusion of solvent. Implicit solvent included via a polarizable continuum approach was found to be sufficient in reproducing the excitation energies accurately in the majority of cases. Moreover, we found that the SMD solvent model, which is dependent on the full electron density of the solute without partitioning into partial charges, gave more reliable results for our systems relative to the conductor-like polarizable continuum model (CPCM), as implemented in Gaussian 09. In all cases the inclusion of solvent reduces the error in the predicted excitation energy to <0.3 eV and in the majority of cases to <0.1 eV.

scholarly journals The ANI-1ccx and ANI-1x Data Sets, Coupled-Cluster and Density Functional Theory Properties for Molecules

2020 ◽  
Author(s):  
Justin S. Smith ◽  
Roman Zubatyuk ◽  
Benjamin T. Nebgen ◽  
Nicholas Lubbers ◽  
Kipton Barros ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Atomic Charge ◽  
Density Functional Theory Calculations ◽  
Coupled Cluster ◽  
Data Sets ◽  
Data Set ◽  
Functional Theory ◽  
Energy Surfaces

<p>Maximum diversification of data is a central theme in building generalized and accurate machine learning (ML) models. In chemistry, ML has been used to develop models for predicting molecular properties, for example quantum mechanics (QM) calculated potential energy surfaces and atomic charge models. The ANI-1x and ANI-1ccx ML-based eneral-purpose potentials for organic molecules were developed through active learning; an automated data diversification process. Here, we describe the ANI-1x and ANI-1ccx data sets. To demonstrate data set diversity, we visualize them with a dimensionality reduction scheme, and contrast against existing data sets. The ANI-1x data set contains multiple QM properties from 5M density functional theory calculations, while the ANI-1ccx data set contains 500k data points obtained with an accurate CCSD(T)/CBS extrapolation. Approximately 14 million CPU core-hours were expended to generate this data. Multiple QM properties from density functional theory and coupled cluster are provided: energies, atomic forces, multipole moments, atomic charges, and more. We provide this data to the community to aid research and development of ML models for chemistry.</p>

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