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1

Thermodynamic and Electronic Properties of OsB_2 from First-Principles Calculations

100%

Cheng Y., Yang J., Wang Y., Ji G., Chen X.

Acta Physica Polonica A

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2014

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vol. 125

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issue 5

1186-1190

EN

The pressure induced phase transitions of OsB_2 from the orthorhombic structure (Orth) to the hexagonal structure (Hex) is investigated by using ab initio plane-wave pseudopotential density functional theory, together with quasi-harmonic Debye model. We find that the pressure-induced phase transition occurs at 2.8 GPa and 12.5 GPa by local density approximation and general gradient approximation, respectively. It is predicted that OsB_2 has no phase transition temperature from the Orth structure to the Hex structure. Moreover, the dependences of the relative volume V/V_0 on the pressure, thermal expansion coefficient α on the pressure and temperature are also successfully obtained. The electronic properties including energy band, total and partial density of states and electron density difference for two structures are also analyzed. The Mulliken charges and Bond populations for both Orth and Hex structures are also obtained.

2

A Microscopic Study of One-Dimensional Solid ^4He Using the Static Fluctuation Approximation

100%

Alhami E., Al-Sugheir M., Ghassib H.

Acta Physica Polonica A

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2015

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vol. 127

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issue 6

1648-1656

EN

In this work, solid helium is studied within the framework of the static fluctuation approximation. The closed set of nonlinear coupled equations, which is an inherent feature of this approximation, is derived for one-dimensional solid ^{4}He. This set is solved numerically by an iteration method for a realistic interhelium potential. The central aim is to determine the chemical potential μ , condensate fraction N_{0}/N, total energy U, heat capacity C, and entropy S of the system. The effects of temperature T, total number of particles N, frequency ω and lattice constant R on these properties are emphasized and explained. Below 80 mK: (1) as N or ω increases, μ increases; (2) as N increases, U, C, and S increase; whereas N_{0}/N, U/N, C/Nk_{B} and S/Nk_{B} decrease (k_{B} being Boltzmann's constant); (3) as ω increases, N_{0}/N, U, C, and S increase; whereas U/N, C/Nk_{B} and S/Nk_{B} are hardly affected; and (4) as T → 0, the effect of R on N_{0}/N increases. These results are presented in a set of figures.

3

Bose-Einstein Condensation of Hard Sphere Homogeneous Gas in Static Fluctuation Approximation

88%

Al-Sugheir M., Gasymeh S., Shatnawi M., Bawa'aneh M.

Acta Physica Polonica A

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2009

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vol. 116

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issue 2

154-156

EN

The condensation fraction, transition temperature, and energy per particle for a hard sphere interacting homogeneous Bose gas using the static fluctuation approximation have been determined. The transition temperature at liquid helium density has been found to be lower than that for the noninteracting gas. Both superfluidity and the Bose-Einstein condensation have been found to occur at the same transition temperature. Our results are consistent with results obtained by other methods.

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Thermodynamic and Electronic Properties of OsB_2 from First-Principles Calculations

A Microscopic Study of One-Dimensional Solid ^4He Using the Static Fluctuation Approximation

Bose-Einstein Condensation of Hard Sphere Homogeneous Gas in Static Fluctuation Approximation