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Search Results: 1 - 10 of 1881 matches for " ab initio results "
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Ab initio determination of the (100) surfaces phonon dispersions of the SiC
Soares, J. S.;Alves, H. W. Leite;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300018
Abstract: in this work, we presented our preliminary ab initio results for the vibrational modes and the phonon frequencies of the sic (100) surfaces. our results are in good agreement with the available experimental data whenever this comparison is possible. for the accepted models of the c-terminated surfaces in the c(2×2) reconstruction, while in the bridge-dimer model there is an acetylene-like vibrational a1 mode at 2031 cm-1, which is infrared active, in the staggered-dimer model, there is a füchs-kliewer (fk) mode at 1328 cm-1, which is experimentally detected. for si-terminated surfaces in the p(2×1) reconstruction, instead, no fk was obtained, in contradiction with the hreels experimental results for the si-terminated surfaces, but they are in consonance with the fact that this surface should be described by a (3×2) or more complex models.
Structural and electronic properties of the SiC (100) surfaces
Soares, J. S.;Alves, H. W. Leite;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300017
Abstract: in this work, we present our preliminary ab initio results for the structural and electronic properties of both si- and c-terminated sic (100) surfaces in (2×1) and c(2×2) reconstruction patterns. based on our results, we found that the si-terminated surfaces are dominated by weak bonded si-dimers, which are stabilized only at si-rich conditions, leading to (3×2) or more complex reconstruction patterns, as verified experimentally. also, our results show that the c-terminated surfaces is characterized by strong triply-bonded c-dimers, in a c(2×2) reconstruction pattern, which consists of c2 pairs over si bridge sites, in agreement with experimental results.
Investigation of the Stability of Oxadiasole and Their Analogs Using Quantum Mechanics Computation  [PDF]
Masoud Karimi
Computational Chemistry (CC) , 2016, DOI: 10.4236/cc.2016.41002
Abstract: This study aimed at investigating factors affecting the stability as well as structural properties of different Oxadiasole and Thiadiasole isomers based on theoretical level B3LYP/6-311+G**, Nuclear Magnetic Resonance (NMR), and Nucleus-independent Chemical Shift (NICS). Qualitative relationships between relative stabilities of 1,2,3-Oxadiazole, 1,2,4-Oxadiazole, 1,2,5-Oxadiazole and 1,3,4-Oxadiazole were obtained. Aromatic stabilization energy (ASE), aromatic ring current (NICS), HUMO-LUMO gaps, electro-negativity (X), hardness (η), softness (S), electro-philicity (ω) and structural parameters were also calculated in the same theoretical level. The results show that 1,3,4-Oxadiazole is more stable than 1,2,3-Oxadiazole, 1,2,4-Oxadiazole and 1,2,5-Oxadiazole. Unlike the trends observed in Oxadiazoles, 1,2,5-Thiadiazole isomer is more stable than other corresponding Isomers.
Vibrational contribution to dipole polarizability and first hyperpolarizability of LiH
Costa, Marcello F.;Ribeiro, Mauro C. C.;
Química Nova , 2006, DOI: 10.1590/S0100-40422006000600023
Abstract: the role played by electron correlation and vibrational correction on the polarizability of the lih molecule is demonstrated. we present results for the dipole moment, polarizability and first hyperpolarizability of the lih molecule obtained through many-body perturbation-theory, coupled-cluster and quadratic configuration interaction methods. our best result for the dipole polarizability, obtained using the qcisd(t) scheme, indicates that the vibrational contribution is appreciable, amounting to ca. 10% of the total polarizability. regarding the first hyperpolarizability, the vibrational contribution is even more important and has opposite sign in comparison with the electronic contribution.
Estudio de la superficie diabática correspondiente a los estados excitados del dímero N2-He
Llanos, M;López-Planes, R;Hernández, A;Salazar, M;
Revista mexicana de física , 2006,
Abstract: the potential energy surface of n2-he dimmer is calculated by supermolecule approximation with m?ller-plesset perturbation theory of fourth level (mppt4), up model rigid rotor. we have obtain of the diabatic surface n2(a1iig)-he(1s) of distance of equilibrium re= 6.10 u.a., their interaction of potential give the deep of well de = 36.25 cm-1.
A model study on the stacking interaction of phenanthroline ligand with nucleic acid base pairs: An ab initio, MP2 and DFT studies  [PDF]
Pankaj Hazarika, Bipul Bezbaruah, Pranjali Das, Okhil Kumar Medhi, Chitrani Medhi
Journal of Biophysical Chemistry (JBPC) , 2011, DOI: 10.4236/jbpc.2011.22019
Abstract: The stacking of phenanthroline(phen) ligand within base pair sequences is one of the important factors for the stabilization of metalphen complex within DNA. The stacking ability of this ligand has been assessed to deduce the base pair selectivity as well as to identify the favored region of intercalation. Different level of theories have been used to predict the favorable regions for stacking interaction of phen ligand with base pair, but the results of MP2/6-31+G(d,p) is found to be reasonably good for monitoring such interactions.
A quantum-chemical model of the inhibition mechanismof viral DNA HIV-1 replication by Iodine complexcompounds  [PDF]
Gulnara A. Yuldasheva, Georgii M. Zhidomirov, Aleksandr I. Ilin
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.37080
Abstract: The interaction of molecular iodine with virus DNA nucleotide is studied by ab initio RHF/3-21G** method. Formation of the nucleoprotein complex of the HIV DNA, molecular iodine and the HIV-1 integrase co-factor is considered to cause the inhibition action of the integrase enzyme. Experimental data on the anti-HIV effect of the molecular iodine complex compounds and the results of calculations suggest that molecular iodine contained in iodine polymer complexes may be considered as a compound inhibiting the catalytic center of the integrase enzyme. Unlike the known integrase inhibitors, molecular iodine also changes the virus DNA structure and produces the N-I bond in the purine bases of adenosine and guanosine nucleotides.
First Principle Study of Cubic SrMO3 Perovskites (M = Ti, Zr, Mo, Rh, Ru)  [PDF]
Avinash Daga, Smita Sharma, K. S. Sharma
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.28095
Abstract: Lattice parameter and corresponding total free energy have been computed for cubic SrMO3 perovskites (M = Ti, Zr, Mo, Rh, Ru) using the first principle approach within Density functional theory. The results have been calculated using local density approximation (LDA) method. It is found that the calculated lattice parameter for all transition metal oxides are in good agreement with the available experimental data. The total free energy corresponding to this lattice constant has been calculated along with different components of the total free energy. All these calculations have been carried out using ABINIT computer code.
First Principles Study of Structural and Electronic Properties of OxS1-xZn Ternary Alloy  [PDF]
Mohammed Ameri, Daho Salah Eddine, Mokhtar Sebane, Keltouma Boudia, Yarub Al-Douri, Ali Bentouaf, Djelloul Hachemane, Bachir Bouhafs, Amina Touia
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.41008

We perform self-consistent ab-initio calculations to study the structural and electronic properties of zinc blende ZnS, ZnO and their alloy. The full-potential muffin-tin orbitals (FP-LMTO) method was employed within density functional theory (DFT) based on local density Approximation (LDA), and generalized gradient approximation (GGA). We analyze composition effect on lattice constants, bulk modulus, band gap and effective mass of the electron. Using the approach of Zunger and coworkers, the microscopic origins of band gap bowing have been detailed and explained. Discussions will be given in comparison with results obtained with other available theoretical and experimental results.

Recalculate Structural, Elastic, Electronic, and Thermal Properties in LaAlO3 Rhombohedral Perovskite  [PDF]
Abdelkader Boudali, Fatiha Saadaoui, Mostefa Zemouli, Mohamed Driss Khodja, Kadda Amara
Advances in Materials Physics and Chemistry (AMPC) , 2013, DOI: 10.4236/ampc.2013.32020

We study the structural, elastic and electronic properties of perovskite insulator LaAlO3 using two different methods: the full-potential linearized augmented plane wave method and the pseudo-potential plane wave scheme in the frame of generalized gradient approximation and local density approximation GGA + mBJ. We have evaluated the ground state quantities. Also, we have presented the results of the band structure and densities of states. These results are in favourable agreement with previous theoretical works and the existing experimental data. To complete the fundamental characteristics of this compound, we have analyzed the thermodynamic properties.

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