scholarly journals Free Energy of Metals from Quasi-Harmonic Models of Thermal Disorder

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 195
Author(s):  
Pavel A. Korzhavyi ◽  
Jing Zhang
Keyword(s):  
Free Energy ◽  
First Principles ◽  
Density Functional ◽  
Helmholtz Free Energy ◽  
Complex Materials ◽  
Predictive Capability ◽  
Temperature Dependent ◽  
Disordered Alloys ◽  
Thermal Disorder ◽  
Structure Calculations

A simple modeling method to extend first-principles electronic structure calculations to finite temperatures is presented. The method is applicable to crystalline solids exhibiting complex thermal disorder and employs quasi-harmonic models to represent the vibrational and magnetic free energy contributions. The main outcome is the Helmholtz free energy, calculated as a function of volume and temperature, from which the other related thermophysical properties (such as temperature-dependent lattice and elastic constants) can be derived. Our test calculations for Fe, Ni, Ti, and W metals in the paramagnetic state at temperatures of up to 1600 K show that the predictive capability of the quasi-harmonic modeling approach is mainly limited by the electron density functional approximation used and, in the second place, by the neglect of higher-order anharmonic effects. The developed methodology is equally applicable to disordered alloys and ordered compounds and can therefore be useful in modeling realistically complex materials.

Ab Initio Electronic Structure Studies of CuO Multiferroics

2012 ◽  
Vol 488-489 ◽  
pp. 129-132 ◽  
Author(s):  
C. Kanagaraj ◽  
Baskaran Natesan
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Metallic State ◽  
Magnetic Ground State ◽  
Electronic Band ◽  
Functional Theory ◽  
High Tc ◽  
Band Structure Calculations ◽  
Structure Calculations

We have performed detailed structural, electronic and magnetic properties of high - TC multiferroic CuO using first principles density functional theory. The total energy results revealed that AFM is the most stable magnetic ground state of CuO. The DOS and electronic band structure calculations show that in the absence of on-site Coulomb interaction (U), AFM structure of CuO heads to a metallic state. However, upon incorporating U in the calculations, a band gap of 1.2 eV is recovered. Furthermore, the Born effective charges calculated on Cu does not show any anomalous character.This suggests that the polarization seen in CuO could be attributed to the spin induced AFM ordering effect.

scholarly journals First-principles study on electronic, optic, elastic, dynamic and thermodynamic properties of RbH compound

2015 ◽  
Vol 6 ◽  
pp. A6 ◽  
Author(s):  
Sinem Erden Gulebaglan ◽  
Emel Kilit Dogan ◽  
Mehmet Nurullah Secuk ◽  
Murat Aycibin ◽  
Bahattin Erdinc ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
Band Gap ◽  
Lattice Constant ◽  
First Principles ◽  
Density Functional ◽  
Temperature Dependent ◽  
Functional Theory ◽  
Salt Structure ◽  
Elastic Lattice ◽  
Good Agreement

We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied.

Study on CH4 Adsorption onto the Surfaces of Perovskite ABO3 ( A=La, Ba; B=Zr, Co, Ce) by Density Functional Theory

2011 ◽  
Vol 291-294 ◽  
pp. 1208-1211 ◽  
Author(s):  
Zi Shu Gao ◽  
Hua An ◽  
Li Lv ◽  
Li Chun Hou ◽  
Hui Han ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Energy State ◽  
Absorption Mechanism ◽  
Functional Theory ◽  
Key Factor ◽  
A Site ◽  
Perovskite Type ◽  
Structure Calculations

The adsorption of CH4onto the surfaces of perovskite-type catalysts ABO3( A=La, Ba; B=Zr, Co, Ce) was investigated by a density functional theory based on the first-principles in this paper. The absorption mechanism was derived by population and electronic states analysis on the basis of the electronic and surface structure calculations. For A=Ba and B=Zr, the frontier energy state was found to the key factor in controlling the adsorption behavior of CH4absorbed on (001) surfaces, which is mainly contributed by oxygen and B-site ions. The most favorite adsorption site for CH4was located at B-sites of perovskite catalysts ABO3, where the A-site ions adjust the charge of B-site ions and moreover affect the CH4adsorption.

scholarly journals Determination of Silicon Electrical Properties Using First Principles Approach

2021 ◽  
Vol 2129 (1) ◽  
pp. 012056
Author(s):  
Uda Hashim ◽  
Tijjani Adam ◽  
M N Afnan Uda ◽  
M N A Uda
Keyword(s):  
Band Gap ◽  
Silicon Nanowires ◽  
First Principles ◽  
Density Functional ◽  
Energy Gap ◽  
Silicon Nanowire ◽  
Continuum Theory ◽  
Simple Extrapolation ◽  
Structure Calculations

Abstract Silicon nanowires have attracted attention as basis for reconfigurable electronics. However, as the size decreases, the electronic properties of the nanowires vary as a result of confinement, strain and crystal topology effects. Thus, at the thin diameter regime the band gap of Silicon nanowires can no longer be derived from a simple extrapolation of the isotropic bulk behaviour. This study compares band gap parameters in sub 10nm nanowires obtained from first-principles density-functional band structure calculations with extrapolations using continuum theory in order to rationalize the changes of the overall conductance, resistance and band gap. The device consists of silicon nanowire of size between 1 nm to 6nm. The results indicate an increase of, both the energy gap and the resistance along with reduced conductivity for the thinnest wires and a dependence on the crystal orientation with gaps reaching up to 4.3 eV along <111>, 4.0 eV along <110>, and 3.7 along <100>.

Theoretical study of thermodynamic properties for SmAlO3 under the effects of pressure and temperature

2018 ◽  
Vol 32 (23) ◽  
pp. 1850247 ◽  
Author(s):  
Ghulam Mustafa ◽  
Ahmad Afaq ◽  
Najm Ul Aarifeen ◽  
Muhammad Asif ◽  
Jamil Ahmad ◽  
...  
Keyword(s):  
Free Energy ◽  
Thermodynamic Properties ◽  
Bulk Modulus ◽  
Internal Energy ◽  
Debye Temperature ◽  
Density Functional ◽  
Helmholtz Free Energy ◽  
Coefficient Of Thermal Expansion ◽  
Temperature Limit ◽  
Debye Model

In the present paper, we have investigated SmAlO3 for their thermodynamic properties under effect of pressure and temperature by employing density functional theory (DFT) and quasi-harmonic Debye model. The various thermodynamic properties like Bulk Modulus, entropy, internal energy, Helmholtz free energy, Debye temperature, coefficient of thermal expansion, Grüneisen parameter and heat capacities of the ternary alloy are calculated. We found that Bulk Modulus, Debye temperature and Helmholtz free energy have decreasing trend with rise of temperature while their values have increasing behavior with rise of pressure. The internal energy of the system almost remains same with variation in pressure but temperature effectively increasing it. Our results are in good agreement with available data at low-temperature limit.

Thermoelastic Generalization of Isothermal Elastic Constitutive Models for Rubber-Like Materials

1996 ◽  
Vol 69 (2) ◽  
pp. 313-324 ◽  
Author(s):  
Nianning Zeng ◽  
Henry W. Haslach
Keyword(s):  
Free Energy ◽  
Thermal Properties ◽  
Helmholtz Free Energy ◽  
Constitutive Models ◽  
Temperature Dependent ◽  
Thermal Inversion ◽  
Entropic Elasticity ◽  
Deformation Dependence ◽  
Constant Deformation ◽  
Inversion Effects

Abstract Existing thermoelastic constitutive models are not able to predict important thermal properties of rubbers. For example, the modified entropic elasticity theory fails to predict that the temperature coefficient of stress, the energetic contribution to the stress, and the specific heat at constant deformation depend on both deformation and temperature. A class of thermoelastic constitutive equations is proposed that generalizes given isothermal models and predicts the temperature and deformation dependence. The Helmholtz free energy is written as the sum of the isothermal energy function, but with temperature-dependent material moduli, and a function of temperature. Conditions on the Helmholtz energy are given to ensure that three inversion effects which characterize rubber are predicted. As an application, an isotropic, homogeneous, mechanically incompressible thermoelastic constitutive equation is generalized from the isothermal Mooney-Rivlin model. The three uniaxial thermal inversion effects are successfully reproduced by this model.

First-principles study of the stability of silicane and germanane under strain

2014 ◽  
Vol 28 (17) ◽  
pp. 1450138 ◽  
Author(s):  
T. Y. Du ◽  
J. Zhao ◽  
G. Liu ◽  
J. X. Le ◽  
B. Xu
Keyword(s):  
First Principles ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Tensile Strain ◽  
Helmholtz Free Energy ◽  
Compressive Strain ◽  
Specific Capacity ◽  
Biaxial Strain ◽  
Functional Theory ◽  
The Stability

In this paper, we investigate the structural stability of silicane and germanane under biaxial strain by employing the lattice dynamics calculations within the frame of density functional theory. Our results show that silicane and germanane become unstable even under 1% compressive strain, while maintaining stable under tensile strain. Further calculations about the thermodynamical properties of silicane and germanane show that the phonon contribution to Helmholtz free energy, entropy and specific capacity are insensitive to the tensile strain.

Ab initio study of thermodynamic properties of bulk zinc-blende CdS: Comparing the LDA and GGA

2018 ◽  
Vol 32 (20) ◽  
pp. 1850207 ◽  
Author(s):  
Fatemeh Badieian Baghsiyahi ◽  
Arsalan Akhtar ◽  
Mahboubeh Yeganeh
Keyword(s):  
Free Energy ◽  
Thermal Expansion ◽  
Thermodynamic Properties ◽  
Bulk Modulus ◽  
Internal Energy ◽  
Density Functional ◽  
Helmholtz Free Energy ◽  
Constant Volume ◽  
Grüneisen Parameter ◽  
Zinc Blende

In the present study, we have investigated the phonon and thermodynamic properties of bulk zinc-blende CdS by first-principle calculations within the density functional theory (DFT) and the density functional perturbation theory (DFPT) method using the quasi harmonic approximation (QHA). We calculated the phonon dispersion at several high symmetry directions, density of phonon state, temperature dependence feature of Helmholtz free energy (F), internal energy, bulk modulus, constant-volume specific heat, entropy, coefficient of the volume thermal expansion and Grüneisen parameter estimated with the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential and compared them with each other. For internal energy, Helmholtz free energy, constant volume heat capacity and phonon entropy the LDA and GGA results are very similar. But, the LDA gives lattice constants that are smaller than GGA while phonon frequencies, bulk modulus and cohesive energies are larger. On the other hand, the results obtained through the GGA approximation for the coefficient of the volume thermal expansion and Grüneisen parameter are larger than those obtained from LDA.

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