scholarly journals Experimental and Computational Vibration Study of Amino Acids

2013 ◽  
Vol 15 ◽  
pp. 1-17 ◽  
Author(s):  
Musa E. Mohamed ◽  
Abdelhafeez M.A. Mohammed
Keyword(s):  
Amino Acids ◽  
Glutamic Acid ◽  
Ab Initio ◽  
Vibrational Frequencies ◽  
Empirical Methods ◽  
Vibrational Studies ◽  
Semi Empirical

Vibrational studies of amino acids experimentally and theoretically have been performed. The Semi-empirical methods optimization by PM6 and RM1 on the l- and d-amino acids (alanine, phenylalanine, aspartic and glutamic acid), showed no difference in energy between l-and d-isomers. The vibrational frequencies were calculated by semi-emprical methods (PM6 and RM1) and Ab Initio methods (B3LYP/6-31+G(d) and were scaled down by factors of 0.925 (RM1), 1.09 (PM6) and 0.89 (B3LYP/6-31+G(d)). The calculated and experimental vibrational frequencies have shown good general agreement.

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 Theoretical Inversion of Amino Acids (Alanine and Aspartic Acid) by Semi-Empirical Methods

2013 ◽  
Vol 12 ◽  
pp. 37-44
Author(s):  
Musa E. Mohamed
Keyword(s):  
Activation Energy ◽  
Amino Acids ◽  
Transition State ◽  
Gas Phase ◽  
Aspartic Acid ◽  
Aqueous Phase ◽  
Free Amino ◽  
Membered Ring ◽  
Empirical Methods ◽  
Semi Empirical

The inversion reaction coordinate of free amino acids (alanine, aspartic acid) have been computationally calculated by semi-empirical methods AM1. A transition state for free alanine and aspartic acid were obtained as a three membered ring in which the α-C-H and α-C-CH3 are slightly elongated, 1.2 and 2.17 Å respectively in the alanine transition state. The activation energy of alanine is 77.52 kcal/mol in the gas phase and 76.66 kcal/mol in aqueous phase, and for aspartic acid is 54.87 kcal/mol in the gas phase and 50.86 kcal/mol in aqueous phase.

scholarly journals Studies on Simulation of Spectra of Some Organic Compounds

2019 ◽  
Vol 35 (6) ◽  
pp. 1655-1668
Author(s):  
Pradeep Kumar Gupta ◽  
Kishor Arora
Keyword(s):  
Ab Initio ◽  
Organic Compounds ◽  
Quantum Chemical ◽  
Theoretical Chemistry ◽  
Simulation Studies ◽  
Empirical Methods ◽  
Present Communication ◽  
Semi Empirical ◽  
Simulation Of Spectra

Quantum chemical viz. ab initio or semi-empirical based simulation studies are now prevailing among workers / scientists pursuing their studies in theoretical chemistry. These studies provide better insight for the compounds so far as the studies of their structural orother parameters are concern. Studies involving the packages developed on the basis of ab-initio or semi-empirical methods are proven to be more effective and as a better tool because of number of their advantages. The present communication includes the studies on synthesis or procurement along with the simulation of spectra viz. I.R. of some heterocyclic organic compounds.

Structure of dicyano-pyridinium methylide and amidocyano-pyridinium methylide using ab initio and semi-empirical methods

1997 ◽  
Vol 435 (1) ◽  
pp. 35-47 ◽  
Author(s):  
Yasser Karzazi ◽  
Gerard Vergoten ◽  
Gheorghe Surpateanu
Keyword(s):  
Ab Initio ◽  
Empirical Methods ◽  
Semi Empirical

Aryl- and alkylnitrenium ions: singlet-triplet gaps via AB initio and semi-empirical methods

1992 ◽  
Vol 33 (13) ◽  
pp. 1705-1708 ◽  
Author(s):  
Daniel E. Favley ◽  
Christopher J. Cramer
Keyword(s):  
Ab Initio ◽  
Empirical Methods ◽  
Semi Empirical

Optical absorption spectra and g factor of MgO: Mn2+explored by ab initio and semi empirical methods

2018 ◽  
Vol 113 ◽  
pp. 194-200 ◽  
Author(s):  
E.-L. Andreici Eftimie ◽  
C.N. Avram ◽  
M.G. Brik ◽  
N.M. Avram
Keyword(s):  
Optical Absorption ◽  
Ab Initio ◽  
Absorption Spectra ◽  
Optical Absorption Spectra ◽  
Empirical Methods ◽  
G Factor ◽  
Semi Empirical
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