From Electronic Structure To Thermodynamics

1987 ◽  
Vol 104 ◽  
Author(s):  
Giovanni B. Bachelet
Keyword(s):  
First Principles ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Preliminary Test ◽  
Computational Effort ◽  
Consistent Theory ◽  
Amorphous Systems ◽  
Trajectory Approach ◽  
Properties Of Materials

ABSTRACTA simple way to extend the remarkable results of Density Functional calculations to finite-temperature properties of materials is the quasi-harmonic theory of Lattice Dynamics. In this framework a thermodynamically consistent theory needs the complete phonon spectrum for a large periodic system (30–100 atoms/cell) at many different volumes, which poses severe practical limitations. In this paper I present the application to a semiconducting system of a method recently proposed by Bachelet and De Lorenzi to overcome these limitations. Based on low-temperature Molecular-Dynamics trajectories (now possible from first principles for semiconducting systems according to the method of Car and Parrinello), the method is shown to provide accurate dynamical matrices for an 8-atom silicon supercell. Such a successful, preliminary test, together with the fact that for larger and/or lower-symmetry systems the computational effort required by the “trajectory approach” is lower than traditional frozen-phonon or force-constant techniques, suggests its use in the determination of dynamical matrices of larger defect or amorphous systems, and thus in the study of their thermodynamics from first principles.

scholarly journals First-Principles Determination of the Polarizabilities of Carbon Tubules as a Function of Length

1994 ◽  
Vol 349 ◽  
Author(s):  
Andrew A. Quong ◽  
Mark R. Pederson
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Valence Electron ◽  
Local Density ◽  
Density Approximation ◽  
Functional Theory ◽  
Size Dependent ◽  
The Density Functional Theory ◽  
Linear And Nonlinear

ABSTRACTWe use the local-density-approximation to the density-functional theory to determine the axial polarizabilities of fullerene tubules as a function of length and winding topologies. Specifically, we present linear polarizabilities for tubules of composition C12H24, C36H24, C40H20 and C60H24. The size-dependent variation in the dipole-coupled gaps between pairs of occupied and unoccupied levels leads to enhancements in the polarizability per valence electron as the length of the tubule increases. The results are compared to recent densityfunctional based calculations of the linear and nonlinear polarizabilities for fullerene and benzene molecules.

THEORETICAL INVESTIGATION OF THE ELASTIC PROPERTIES AND LATTICE DYNAMICS OF THE MgSxSe1-x ALLOY

2007 ◽  
Vol 21 (05) ◽  
pp. 249-259 ◽  
Author(s):  
K. BOUAMAMA ◽  
P. DJEMIA
Keyword(s):  
Elastic Properties ◽  
First Principles ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Local Density ◽  
Lattice Parameter ◽  
First Principles Calculations ◽  
Virtual Crystal Approximation ◽  
Functional Theory ◽  
Density Functional Perturbation Theory

Structural and elastic properties as well as lattice dynamics of ternary MgS x Se 1-x alloy have been studied using first-principles calculations. These are done using density functional theory (DFT) and density functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We found that the lattice parameter, the elastic constants and the phonon frequencies follow a quadratic law in x.

First-principle studies of the lattice dynamics of crystals, and related properties

2005 ◽  
Vol 220 (5/6) ◽  
Author(s):  
Xavier Gonze ◽  
Gian-Marco Rignanese ◽  
Razvan Caracas
Keyword(s):  
Perturbation Theory ◽  
First Principles ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Computational Method ◽  
Dielectric Tensor ◽  
Atomic Temperature ◽  
Density Functional Perturbation Theory ◽  
Infra Red ◽  
Temperature Factors

AbstractThe crystal lattice is never rigid. Due to temperature, external fields or pressure, the nuclei vibrate, the lattice distorts, and instabilities can induce phase transitions. We review the basic concepts of density-functional perturbation theory, a computational method especially suited to determine from first-principles the microscopic parameters governing such behaviour. Then, we present the additional formalism leading to the following properties of minerals: the infra-red and Raman spectra; the prediction of (meta)stability or instability of a crystalline phase, based on the phonon spectrum; the computation of thermodynamics quantities like the free energy, entropy, specific heat; the atomic temperature factors. For each property, examples are given. When appropriate, we mention the computation of related properties, like dielectric tensor and Born effective charges that are needed to get infra-red spectra. Finally, we discuss briefly, on one hand, other applications of the density-functional perturbation theory, and, on the other hand, an alternative technique, the finite-difference computation of dynamical matrices.

Phonon Dispersions of a Single-Wall (8,0) Carbon Nanotube: Effects of the Rotational Acoustic Sum Rule and of Surface Attachment

2004 ◽  
Vol 858 ◽  
Author(s):  
Nicolas Mounet ◽  
Nicola Marzari
Keyword(s):  
Carbon Nanotubes ◽  
First Principles ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Single Walled Carbon Nanotubes ◽  
Vibrational Properties ◽  
Surface Attachment ◽  
Sum Rule ◽  
Density Functional Perturbation Theory ◽  
Walled Carbon Nanotubes

ABSTRACTThe lattice dynamics of single-walled carbon nanotubes (SWCNT) is studied from first-principles using density-functional perturbation theory (DFPT) at the GGA-PBE level. The phonon dispersions of a pristine, infinite zigzag (8,0) SWCNT are obtained and the effect of applying the rotational acoustic sum rule on vibrational properties is discussed. Finally we study the effects of covalent functionalizations on the SWCNT phonon frequencies by selectively increasing the effective mass of the carbon atoms that would link to the functional groups.

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>.

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.

Influence of the core-hole effect on optical properties of magnesium oxide (MgO) near the MgL-edge region

2018 ◽  
Vol 25 (3) ◽  
pp. 771-776 ◽  
Author(s):  
Mangalika Sinha ◽  
Mohammed H. Modi ◽  
Haranath Ghosh ◽  
P. K. Yadav ◽  
R. K. Gupta
Keyword(s):  
Optical Properties ◽  
Magnesium Oxide ◽  
First Principles ◽  
Density Functional ◽  
Optical Constants ◽  
Edge Region ◽  
Core Hole ◽  
The Core ◽  
Hole Effect

The influence of the core-hole effect on optical properties of magnesium oxide (MgO) is established through experimental determination of optical constants and first-principles density functional theory studies. Optical constants (δ and β) of MgO thin film are measured in the spectral region 40–300 eV using reflectance spectroscopy techniques at the Indus-1 synchrotron radiation source. The obtained optical constants show strong core exciton features near the MgL-edge region, causing significant mismatch with Henke's tabulated values. On comparing the experimentally obtained optical constants with Henke's tabulated values, an edge shift of ∼3.0 eV is also observed. Distinct evidence of effects of core exciton on optical constants (δ and β) in the near MgL-edge absorption spectra are confirmed through first-principles simulations.

scholarly journals First-Principles Design of Rutile Oxide Heterostructures for Oxygen Evolution Reactions

2021 ◽  
Vol 9 ◽  
Author(s):  
Hyeong Yong Lim ◽  
Sung O Park ◽  
Su Hwan Kim ◽  
Gwan Yeong Jung ◽  
Sang Kyu Kwak
Keyword(s):  
Oxygen Evolution ◽  
Transition Metal Oxides ◽  
First Principles ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Binding Energies ◽  
Functional Theory ◽  
Oxide Heterostructures

The oxygen evolution reaction (OER) plays a key role in the determination of overall water-splitting rate. Lowering the high overpotential of the OER of transition metal oxides (TMOs), which are used as conventional OER electrocatalysts, has been the focus of many studies. The OER activity of TMOs can be tuned via the strategic formation of a heterostructure with another TMO substrate. We screened 11 rutile-type TMOs (i.e., MO2; M = V, Cr, Mn, Nb, Ru, Rh, Sn, Ta, Os, Ir, and Pt) on a rutile (110) substrate using density functional theory calculations to determine their OER activities. The conventional volcano approach based on simple binding energies of reaction intermediates was implemented; in addition, the electrochemical-step symmetry index was employed to screen heterostructures for use as electrode materials. The results show that RuO2 and IrO2 are the most promising catalysts among all candidates. The scaling results provide insights into the intrinsic properties of the heterostructure as well as materials that can be used to lower the overpotential of the OER.

AB INITIO CALCULATION OF THE LATTICE DYNAMICS OF THE ZnSe1-xTex ALLOY

2009 ◽  
Vol 23 (29) ◽  
pp. 3453-3462
Author(s):  
K. BOUAMAMA ◽  
P. DJEMIA ◽  
N. LEBGA ◽  
K. KASSALI
Keyword(s):  
First Principles ◽  
High Frequency ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Local Density ◽  
High Symmetry ◽  
First Principles Calculations ◽  
Symmetry Point ◽  
Virtual Crystal Approximation ◽  
Density Functional Perturbation Theory

The lattice dynamics of the ternary ZnSe 1-x Te x alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ω TO and ω LO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.

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