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1
Content available remote

Quantum Monte Carlo vs. Density Functional Methods for the Prediction of Relative Energies of Small Si-C Clusters

100%
Gonzalez Szwacki N., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
964-966
EN
In the present paper, we assess the accuracy of popular and widely used approaches based on density functional theory by relating them to the most accurate at present quantum Monte Carlo calculations. As the test case, we consider the relative stability of small Si_{n}C_{m} isomers. We find out that none of the studied DFT approaches employing local, semilocal, or even hybrid functionals are able to predict correctly the relative stability of the isomers.
2
Content available remote

IINS, FT-IR and DFT Study of the Internal Dynamics of [4-apyH][SbCl_4]

80%
Hołderna-Natkaniec K., Natkaniec I., Mikuli E., Swiergiel J., Khavryutchenko V., Jakubas R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 4
1117-1130
EN
A combination of infrared and inelastic incoherent neutron scattering spectroscopies with the density functional theory and semi-empirical calculations was applied to propose an assignment of the vibrational spectra of 4-aminopyridine chloroantimonate(IV).
3
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Structure and Vibrational Studies of ±1-(1H-Benzoimidazol-2-YL) Ethanol, Using DFT Method

80%
Oturak H., Kaya Kinaytürk N., Şahın G.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2B
B-417-B-421
EN
In this study, conformational analysis and quantum chemical calculations of ±1-(1H-Benzoimidazol-2-YL) Ethanol were carried out. The geometric structure, infrared intensities, UV-VIS spectrum, HOMO-LUMO energies, ^1H and ^{13}C nuclear magnetic resonance (NMR) chemical shifts were calculated by using the density functional method (DFT/B3LYP) with 6-311++G(d,p) basis set. The vibrational studies were interpreted in terms of potential energy distribution (PED). Finally, calculated values were compared with the experimental ones.
4
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H₂ Interaction with rm C₂H₂TM (TM = Sc, Ti, V) Complex Using Quantum Chemical Methods

80%
Tavhare P., Wadnerkar N., Kalamse V., Chaudhari A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1257-1262
EN
This work reports a comparative study of hydrogen uptake capacity of early transition metal atom (Sc, Ti and V) attached to light acetylene (C₂H₂) substrate. Using density functional theory and second order Møller-Plesset method, we predict that maximum of five, five and four hydrogen molecules will be adsorbed on C₂H₂Sc, C₂H₂Ti and C₂H₂V complex, respectively, with respective gravimetric hydrogen uptake capacity of 12.43, 12, and 9.48 wt%. All the interactions between hydrogen molecules and organometallic complex are found to be attractive. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap shows that the maximum H₂ adsorbed complexes are kinetically stable. The average binding energies per H₂ molecule for these complexes are within the ideal range for hydrogen storage at ambient conditions. Even after maximum hydrogen molecules adsorption on C₂H₂TM complexes, transition metal atoms remain strongly bound to the C₂H₂ substrate. We have obtained temperature and pressure range over which H₂ adsorption on these three complexes is energetically favorable using the Gibbs free energy corrected H₂ adsorption energy.
5
Content available remote

Van Der Waals Density Functionals for Graphene Layers and Graphite

80%
Birowska M., Milowska K., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
845-848
EN
In this communication, we present results of theoretical studies of various systems where Van der Waals interaction plays a considerable role. In the first-principle calculations performed in the density functional theory framework we implement novel functionals accounting for Van der Waals forces and employ to the test cases of graphite and graphene layers. It turns out that this approach provides a solution to the long standing problem of overbinding between graphene layers in bulk graphite, giving the distance between the carbon layers in excellent agreement with experiment. In graphene bilayers, Van der Waals functionals lead to energetic barriers for A-B to A-A ordering of graphene bilayers that are by a factor of two smaller than the barriers obtained with standard functionals. It may be of crucial importance, particularly, if one uses atomistic ab initio methods as a starting point for multi-scale modeling of materials and for determination of effective potentials.
6
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Structural and Electronic Properties of Functionalized Graphene

80%
Milowska K., Birowska M., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
842-844
EN
In the present paper, we study the effects of functionalization of graphene with simple organic molecules OH, and NH_2, focusing on the stability and band gaps of the structures. We have performed DFT calculations for graphene supercells with various numbers of the attached molecules. We have determined adsorption energies of the functionalized graphene mono- and bilayers, the changes in the geometry, and the band structure. We observe the characteristic effects such as rehybridization of the bonds induced by fragments attached to graphene and opening of the graphene band gap by functionalization. We have also studied the dependence of the adsorption energies of the functionalized graphene on the density of the adsorbed molecules. Our calculations reveal that the -OH and -NH_2 groups exhibit the strong cohesion to graphene layers. Further, we determine the critical density of the OH fragments which lead to the opening of the band gap. We also show how to engineer the magnitude of the band gap by functionalizing graphene with NH_2 groups of various concentrations.
7
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Derivation of von Weizsäcker Equation Based οn Green-Gauss Theorem

80%
Romanowski Z., Krukowski S.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
653-655
EN
A simple and short derivation of von Weizsäcker equation for kinetic energy functional is presented. The derivation is based on the Green-Gauss theorem and is valid for one-electron systems. In the proof the asymptotic behavior of wave function for the finite systems was used. Two results important for kinetic energy functional evaluation are also derived as consequences of the Green-Gauss theorem.
8
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Theoretical Studies of Molecular Structures, Infrared Spectra, NBO and NLO Properties of Some Novel 5-arylazo-6-hydroxy-4-phenyl-3-cyano-2-pyridone Dyes

80%
Esme A., Sagdinc S.
Acta Physica Polonica A
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2016
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vol. 130
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issue 6
1273-1287
EN
The optimized geometrical structures, infrared spectra, molecular electrostatic potential, natural bond orbital and nonlinear optical properties of 5-phenylazo-6-hydroxy-4-phenyl-3-cyano-2-pyridoine (1) and 5-(4-bromophenylazo)-6-hydroxy-4-phenyl-3-cyano-2-pyridoine (2) dyes with a detailed study on the azo-hydrazone tautomerism in the ground state have been investigated by density functional theory using B3LYP functional with 6-31G(d,p) basis set. Vibrational modes are assigned with the help of vibrational energy distribution analysis program. Highest occupied molecular orbital and lowest unoccupied molecular orbital energies of the (1) and (2) compounds with azo and hydrazone forms were calculated with the same method and basis set. Molecular parameters like global hardness (η), global softness (σ) and electronegativity (χ) were calculated with the results obtained from the highest occupied and lowest unoccupied molecular orbital energies. Nonlinear optical parameters (mean polarizability (⟨α⟩), the anisotropy of the polarizability (⟨Δα⟩) and the mean first-order hyperpolarizability (⟨β⟩)) of the title compounds were investigated theoretically. The atomic charges, electronic exchange interaction, and charge delocalization of the molecules have been studied by natural bond orbital analysis.
9
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A DFT Study on (001) Thin Slabs of SrTiO_3 and BaTiO_3

80%
Mahmoodi T.
Acta Physica Polonica A
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2015
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vol. 127
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issue 6
1616-1620
EN
In this paper, we studied the relaxation of (001) surface of BaTiO_3 and SrTiO_3 slabs with two termination surfaces and with 3, 5, and 7 layers thickness for each cases, using density functional theory and generalized gradient approximation for exchange-correlation functional and pseudo potential method. We calculated the slab energy and the rate of expansion and contraction of the layers and compare them for different thicknesses. Band structure and density of states for these slabs and for BaTiO_3 and SrTiO_3 bulk were computed to find out the variation of band gap with respect to slab thickness. It is found that in comparison with bulk, in TiO_2 slabs of both materials gap size decreases while in SrO and BaO slabs it increases.
10
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Distribution of Zn in Magnetoelectric Y-Type Hexaferrite

80%
Kouřil K., Chlan V., Štěpánková H., Telfah A., Novák P., Knížek K., Hiraoka Y., Kimura T.
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issue 5
732-733
EN
We employ ^{67}Zn NMR to study distribution of Zn^{2+} in cationic sites of magnetoelectric Y-type hexaferrite single crystal, Ba_{0.5} Sr_{1.5} Zn_2 Fe_{12} O_{22}. The experimental data are interpreted by comparison with NMR spectra simulated from ab initio calculated hyperfine parameters.
11
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Lanthanide Contraction in RENi_5 (RE~=~La, Ce, Nd, Sm, Eu, Gd, Tb,~Yb) Compounds Studied with Band Structure Calculations

80%
Goraus J., Maślankiewicz P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1076-1078
EN
Full potential linearized augmented plane wave band structure calculations were performed for hexagonal RENi_5 (RE = rare earth) compounds in order to investigate reproducibility of lanthanide contraction by ab initio studies. The a and c parameters were optimised using a paraboloid fit, starting from the same initial values for all compounds studied. The trend in lattice parameters across the RE series obtained from the calculations was found to be in general agreement with experimental data. A comparison of results obtained by generalized gradient approximation and generalized gradient approximation with additional Coulomb correlations calculations is presented for several double counting schemes.
12
Content available remote

Fundamental Gaps in Cr_{8}, Cr_{7}Ni and Cr_{7}Cd Molecules

80%
Brzostowski B., Wojciechowski M., Kamieniarz G.
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vol. 126
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issue 1
234-235
EN
In this paper we investigate fundamental gaps of three octametallic Cr-based molecular rings Cr_{8}F_{8}(Piv)_{16}, Cr_{7}NiF_{8}(Piv)_{16} and Cr_{7}CdF_{8}(Piv)_{16} using the SIESTA package. We find that for the ground-state antiferromagnetic configurations, the gap of the homometallic ring is significantly higher than those of the heterometallic rings. In addition, the HOMO and LUMO orbitals are plotted and discussed.
13
Content available remote

First Principles Study of Gas Adsorption Dynamics on Pristine and Defected Graphene

80%
Wlazło M., Majewski J.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-142-A-144
EN
We present the results of ab initio calculations of gas adsorption processes on graphene. Static density functional theory framework is used to obtain adsorption energies of several species on a Stone-Wales defected graphene monolayer. The Van der Waals interaction is taken into account by a semi-empirical correction. Sites closer to the defect are found to induce stronger adsorption compared to sites further away, where the graphene crystal structure is intact. The Car-Parrinello ab initio molecular dynamics simulations are performed at high temperatures. CH₃ is found to be stably physisorbed or chemisorbed at 300 K.
14
Content available remote

First Principles Calculation of ε-Phase of Solid Oxygen

80%
Kamaruddin K., Abedin A., Zabidi N., Yahya M., Taib M., Rosli A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
468-471
EN
The electronic structures of ε-phase of solid oxygen (O₂)₄ are studied within the framework of density-functional theory. The intriguing molecule has been known to have magnetic properties at room temperature by applying pressure. Nevertheless, until now there was no evidence of band structure studied in the antiferromagnetic behaviour of (O₂)₄. We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O₂)₄ could not be seen experimentally, and antiferromagnetic configuration of (O₂)₄ was seen at higher pressure of about 10 GPa. The antiferromagnetic state transforms into the superconducting state as the sample temperature decreases. The results can serve as a useful approximation in studying general features of the electronic structure. The (O₂)₄ clusters are reported in the Raman study, having significant absorption at 1516 cm¯¹ below infrared region.
15
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Study of Y-type Hexaferrite by Means of ^{57}Fe NMR and Electronic Structure Calculations

80%
Chlan V., Kouřil K., Štěpánková H., Řezníček R., Englich J.
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vol. 126
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issue 1
42-43
EN
The electron structure and site preferences of Zn and Fe cations in Y hexaferrite system were calculated. The hyperfine magnetic fields on ^{57}Fe nuclei were determined using WIEN2k and corrections for hyperfine contact interaction. The calculated fields were compared to ^{57}Fe nuclear magnetic resonance (NMR) experiment in Ba_2Zn_2Fe_{12}O_{22} single crystal with an aim of interpretation of experimental NMR spectrum.
16
Content available remote

The Study of Magnetic Molecules Containing Cr₉ Chromium-Based Rings within Density Functional Theory

71%
Brzostowski B., Wojciechowski M., Kamieniarz G.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
961-963
EN
We examine the electronic and magnetic properties of three frustrated Cr₉ molecules with a single bond defect using density functional theory method. Five non-equivalent broken-symmetry spin configurations with S=±3/2 for Cr are considered, the corresponding differences between the total energies are calculated and the exchange interaction parameters J extracted using different scenarios. We find that the couplings for all molecules are antiferrimagnetic. We also estimate the fundamental gaps and in addition, the high occupied molecular orbitals and low occupied molecular orbitals are plotted and discussed.
17
Content available remote

Theoretical Investigation of N-Methyl-N'-(4-nitrobenzylidene) pyrazine-2-carbohydrazide: Conformational Study, NBO Analysis, Molecular Structure and NMR Spectra

71%
Günay N., Tamer Ö., Kuzalic D., Avcı D., Atalay Y.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3
701-710
EN
The crystal structure determination of the methylated pyrazine-2-carbohydrazide derivative, namely N-methyl-N'-(4-nitrobenzylidene)pyrazine-2-carbohydrazide were optimized to obtain its molecular geometric structure and electronic structures at the Hartree-Fock and density functional theory levels (B3LYP) with 6-311G(d,p) and 6-311++G(d,p) basis sets, using Gaussian 09W programme. The ^{1}H and ^{13}C nuclear magnetic resonance chemical shifts of the title molecule were calculated by using the gauge independent atomic orbital, continuous set of gauge transformations and individual gauges for atoms in molecules methods and were also compared with experimental values. The electronic properties high occupied and low unoccupied molecular orbitals energies were calculated and analyzed. Potential energy surface scan, natural population analysis and Mulliken atomic charges were investigated using theoretical calculations. A detailed molecular picture and intermolecular interactions arising from hyperconjugative interactions and charge delocalization of the molecule were analyzed using natural bond orbital analysis.
18
Content available remote

Structural and Spectroscopic Characterization of 1-(5-Bromothiophen-2-yl)-3-(4-nitrophenyl)prop-2-en-1-one: An Analysis of Electronic and NLO Properties

71%
Tamer Ö., Avcı D., Atalay Y.
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vol. 126
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issue 3
679-688
EN
The molecular structure of 1-(5-bromothiophen-2-yl)-3-(4-nitrophenyl)prop-2-en-1-one with C_{13}H_8BrNO_3S empirical formula was simulated using B3LYP and CAM-B3LYP levels of density functional theory. After BTNP was optimized on the ground state, its characterization was enhanced via IR, NMR and UV-vis spectroscopies. Conformational analysis was performed based on B3LYP level so as to find the stable conformers of BTNP. Electronic transitions were calculated, and the important contributions from the molecular orbitals to the electronic transitions were investigated. HOMO and LUMO energies were calculated, and obtained energies displayed that charge transfer occurs in BTNP. It was displayed that BTNP is an efficient NLO material due to the coplanar of phenyl-nitro group and carbonyl group. NBO analysis also proved that charge transfer, conjugative interactions and intramolecular hydrogen bonding interactions occur through BTNP.
19
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First-Principles Calculations of Structural, Electronic, Optical, and Thermodynamic Properties of CdS, CdTe and Their Ternary Alloys CdS_{1-x}Te_{x} (0.0 ≤ x ≤1.0)

71%
Ameri M., Mesbah S., Al-Douri Y., Bouhafs B., Varshney D., Ameri I.
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vol. 125
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issue 5
1110-1117
EN
Using first-principle method, we investigate the structural, electronic, optical, and thermodynamic properties of the CdS_{1-x}Te_x semiconductor alloys using generalized gradient approximation for the exchange-correlation potential calculation. The ground state properties are determined for the bulk materials (CdS and CdTe) in cubic phase. Quantities such as the lattice constants and bulk modulus of interest are calculated. Detailed comparisons are made with published experimental and theoretical data and show generally good agreement. The calculated lattice constants scale linearly with composition (Vegard's law). The microscopic origins of the bowing parameter were explained using the contributions from volume deformation, charge transfer and structural relaxation approach. The refractive index and optical dielectric constant for the alloys of interest were calculated by using different models. In addition, the thermodynamic stability of the alloys was investigated by calculating the critical temperatures of alloys.
20
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Molecular Reorientations οf N-n-Hexyltetrachlorophthalimide Studied by ^1H NMR

71%
Hołderna-Natkaniec K., Jurga K., Woźniak-Braszak A., Walczak A.
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issue 4
537-548
EN
The spin-lattice relaxation times T_{1} and the second moment of ^{1}H NMR line have been employed to study the internal dynamics of protons of N-n-hexyl-tetra-chloro-phthali-mides in the temperature range 80-350 K. The model of internal reorientations has been proposed.
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