scholarly journals QUANTUM MECHANICAL STUDIES OF THE KINETICS, MECHANISMS AND THERMODYNAMICS OF THE GAS-PHASE THERMAL DECOMPOSITION OF ETHYLVINYL ETHER

2013 ◽  
Vol 21 (21) ◽  
pp. 41-60
Author(s):  
I. Ajibade ADEJORO ◽  
O. Olubunmi ADEBOYE
Keyword(s):  
Thermal Decomposition ◽  
Ab Initio ◽  
Density Functional ◽  
Density Functional Method ◽  
Empirical Method ◽  
Ethyl Vinyl Ether ◽  
Ethyl Vinyl ◽  
Exponential Factor ◽  
Parameterized Model ◽  
Semi Empirical

The thermal decomposition of Ethyl Vinyl Ether was studied using Austin Model (AMI), Re-parameterized Austin Model (RMI), Parameterized Model 3 (PM#) and Modified Neglect of Diatomic Overlap (MNDO) Hamiltonian in the Semi-Empirical method, Hartree-Foch at 3-21G,6-31G*, 6-31G** level, and Density Functional method with Becke 3 Lee Yang Parr (B3LYP), 6-31G* in the Ab-initio method of calculation in Spartan '10. The geometric properties such as the bond length, dihedral, bond angles, heat of formation, atomic charges, and vibrational frequencies were obtained. The data were used to calculate the change in enthalpy delta H, entropy deltaS, free energy delta G, pre-exponential factor A, Rate, K at 624K, and the variation of rate, K with temperatures at 498K - 773K at temperature interval of 25K. It was observed that the values obtained are in good agreement with experimental values for both semi-empirical and ab-initio methods and according to Arrhenius Theory, calculated rate K, increases with an increase in temperature.

Relativistic AB Initio calculations of the properties of ionic solids

1986 ◽  
Vol 320 (1553) ◽  
pp. 107-158 ◽  
Keyword(s):  
Ab Initio ◽  
Short Range ◽  
Correlation Energy ◽  
Electron Gas ◽  
Empirical Method ◽  
Coulombic Interactions ◽  
Ionic Solids ◽  
Electron Correlation Energy ◽  
Crystal Properties ◽  
Semi Empirical

Relativistic ab initio calculations of inter-ionic potential energies are used to develop a reliable non-empirical method for predicting the properties of ionic solids containing the heaviest ions. A physically realistic method for describing the non-negligible differences between free and in-crystal ion wavefunctions is described. Functions are presented for describing the partial quenching, arising from ion wavefunction overlap, of the standard long-range form of the inter-ionic dispersive attractions. These attractions are shown to be distinct from the contributions to the inter-ionic potentials that arise from that portion of the electron correlation energy which is nonzero solely because of overlap of the ion wavefunctions. The results presented for NaCl, MgO and the fluorides of Li, Na, Ag and Pb show that these modifications overcome the deficiencies of previous calculations. Ab initio predictions of the closest cation-cation and anion-anion short-range interactions, which are not available from semi-empirical fits to experimental data, are presented. The non-point coulombic interactions between pairs of anions, derived by adding the dispersive attractions to the short-range interactions, are compared with previous semi-empirical and approximate ab initio results. The uncorrelated short-range inter-ionic potentials computed exactly are compared with those predicted from electron-gas theory. The use of the electron-gas approximation to describe any of these potentials degrades the quality of the predicted crystal properties.

scholarly journals STRUCTURAL AND ELECTRONIC PROPERTIES OF BRIDGED BITHIOPHENE S-OXIDES (BTO) WITH S, S=O, O, SiH2 and BH2 BRIDGE: SEMI-EMPIRICAL AND AB INITIO STUDY

2010 ◽  
Vol 18 (18) ◽  
pp. 1-10
Author(s):  
Banjo Semire ◽  
Isaiah Ajibade Adejoro ◽  
Olusegun Ayobami Odunola
Keyword(s):  
Density Functional Theory ◽  
Thermodynamic Properties ◽  
Ab Initio ◽  
Density Functional ◽  
Ab Initio Study ◽  
Empirical Methods ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Semi Empirical ◽  
Good Agreement

In this paper, we theoretically studied the geometries, stabilities, electronic and thermodynamic properties of bridged bithiophene S-oxide (BTO-X) derivates (with X = BH2, SiH2, S, S=O, and O) by using semi-empirical methods, ab-initio, and Density functional theory. The geometries and thermodynamic parameters calculated by PM3 were in good agreement with that of B3LYP/6-31G(d). The bandgap calculated by B3LYP/6-31G(d) ranged from 3.94eV (BTO-O)-3.16eV (BTO-BH2). The absorption λmax calculated suing B3LYP/6-31G(d) shifted to longer wavelength with X=BH2, SiH2, and S=O due to enhancement of π-conjugated system whereas, BTO-S and BTO-O shifted to shorter wavelengths as compared to dimmer thiophene S-oxide (2TO).

scholarly journals Density functional tight binding: values of semi-empirical methods in an ab initio era

2014 ◽  
Vol 16 (28) ◽  
pp. 14368-14377 ◽  
Author(s):  
Qiang Cui ◽  
Marcus Elstner
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Empirical Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Semi Empirical

Semi-empirical (SE) methods are derived from Hartree–Fock (HF) or Density Functional Theory (DFT) by neglect and approximation of electronic integrals.

scholarly journals THEORETICAL METHODS OF NANOSTRUCTURES INVESTIGATION

2017 ◽  
Vol 18 (9) ◽  
pp. 106-117
Author(s):  
I.N. Saliy ◽  
A.S. Kolesnikova ◽  
O.E. Glukhova ◽  
I.V. Kirillova ◽  
E.L. Kossovich ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Ab Initio Methods ◽  
Empirical Methods ◽  
Theoretical Methods ◽  
Basic Concepts ◽  
Semi Empirical

In this work, a review is presented concerning the most modern theoretical methods aimed at investigation of various nanostructures properties. The basic concepts of ab initio methods, density functional, semi-empirical and empirical methods are considered. The applicability boundaries of calculation schemes utilized in the aforementioned methods are denoted.

scholarly journals Excited Multiplets of Eu in GaN

2011 ◽  
Vol 1290 ◽  
Author(s):  
Ben Hourahine
Keyword(s):  
Rare Earth ◽  
Density Functional ◽  
Density Functional Method ◽  
Relative Energy ◽  
Functional Method ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Excitation Mechanism ◽  
Empirical Density ◽  
Semi Empirical

ABSTRACTA method to calculate the multiplet states of lanthanide impurities in solids is presented. This approach is based on a semi-empirical density functional method which includes corrections to account for the correlation and spin-orbit coupling of the 4f electrons. Specific multiplet states of the rare earth are produced by constraining the system. This approach is then used to investigate some of the properties of substitutional europium impurities in gallium nitride, reproducing the relative energy of two multiplets, and discussing a potential excitation mechanism for these centers.

scholarly journals Ab initio-driven nuclear energy density functional method

2015 ◽  
Vol 51 (12) ◽  
Author(s):  
T. Duguet ◽  
M. Bender ◽  
J. -P. Ebran ◽  
T. Lesinski ◽  
V. Somà
Keyword(s):  
Energy Density ◽  
Ab Initio ◽  
Density Functional ◽  
Nuclear Energy ◽  
Density Functional Method ◽  
Functional Method ◽  
Energy Density Functional
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