Dr. Fahmida Parvin - Academia.edu (original) (raw)

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Papers by Dr. Fahmida Parvin

Solid State Communications, 2007

Novel extended tetrahedral forms of CO 2 have been synthesized recently under high-pressure condi... more Novel extended tetrahedral forms of CO 2 have been synthesized recently under high-pressure conditions. We perform ab initio density functional theory calculations to investigate whether doping with Si can extend the stability range of such tetrahedral forms of CO 2 to ambient pressure. Calculations are performed with a simple cubic cell containing eight formula units in a β-cristobalite-like structure. Though we find that all the Si x C 1−x O 2 structures considered by us are thermodynamically unstable with respect to decomposition into the end members at ambient pressures, the energy differences are small, suggesting that it might be possible for such phases to exist in metastable forms. At higher pressures, the heat of formation is found to be negative. The bonding between C and O atoms is more covalent than that between Si and O atoms. We also find indications that some C atoms may prefer threefold coordination at low pressure.

We present first-principles density functional theory (DFT) investigations of mechanical, thermod... more We present first-principles density functional theory (DFT) investigations of mechanical, thermodynamic and optical properties of synthesized inverse-perovskites Sc 3 InX (X = B, C, N). The elastic constants at zero pressure and temperature are calculated and the anisotropic behavior of the compounds is illustrated. All the three materials are shown to be brittle in nature. The computed Peierls stress, approximately 3 to 5 times larger than of a selection of MAX phases, show that dislocation movement may follow but with much reduced occurrences compared to these MAX phases. The Mulliken bonding population and charge density maps show stronger covalency between Sc and X atoms compared with Sc-Sc bond. The Vickers hardness values of Sc 3 InX are predicted to be between 3.03 and 3.88 GPa. The Fermi surfaces of Sc 3 InX contain both hole-and electron-like topology which changes as one replaces B with C or N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye temperature are calculated as a function both temperature and pressure using the quasi-harmonic Debye model with phononic effects. The results so obtained are analysed in comparison to the characteristics of other related compounds. Moreover optical functions are calculated and discussed for the first time. The reflectivity is found to be high in the IR-UV regions up to ~ 10.7 eV (Sc 3 InB, Sc 3 InC) and 12.3 eV (Sc 3 InN), thus showing promise as good coating materials.

The European Physical Journal B, 2018

Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic ... more Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb 3 B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied in detail for the first time. Vickers hardness of these compounds is also studied. The Fermi surfaces of Nb 3 B contain both holeand electron-like sheets, the features of which change systematically as one move from Os to Au. The electronic charge density distribution implies that Nb 3 Os, Nb 3 Pt and Nb 3 Au have a mixture of ionic and covalent bondings with a substantial metallic contribution. The charge transfer between the atomic species in these compounds has been explained via the Mulliken bond population analysis and the Hirshfeld population analysis. The bonding properties show a good correspondence to the electronic band structure derived electronic density of states (DOS) near the Fermi level. Debye temperature of Nb 3 B (B = Os, Pt, Au) have been estimated from the elastic constants and show a systematic behavior as a function of the B atomic species. We have discussed implications of the results obtained in this study in details in this paper.

Journal of Scientific Research, 2010

Two possible phases of superhard material BC3 originating from the cubic diamond structure are in... more Two possible phases of superhard material BC3 originating from the cubic diamond structure are investigated by ab initio pseudopotential density functional method using generalized gradient approximation (GGA). We calculate their elastic constants, electronic band structure, and density of states (DOS). Full phonon frequencies, electron-phonon coupling constant and possible superconducting Tc of the metallic phase with tetragonal symmetry (t-BC3, space group P-42m) have for the first time been investigated at 5 and 10 GPa. The calculated electron-phonon coupling (0.67) and the logarithmically-averaged frequency (862 cm-1) show superconductivity for the undoped t-BC3 with Tc = 20 K at 5 GPa, which decreases to 17.5 K at 10 GPa. Keywords: Superhard BC3; Band structure; Phonon spectra; Superconductivity. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v2i2.2638 J. Sci. Res. 2 (2), 203-213 (2010)

Physica C: Superconductivity and its Applications, 2014

A new superconductor (Na 0.25 K 0.45)Ba 3 Bi 4 O 12 , having an A-site-ordered double perovskite ... more A new superconductor (Na 0.25 K 0.45)Ba 3 Bi 4 O 12 , having an A-site-ordered double perovskite structure, with a maximum T c ~ 27 K has very recently been discovered through hydrothermal synthesis at 593 K. The structural, elastic, electronic, and thermal properties of the new synthesized compound have been investigated theoretically. Here we have employed the pseudo-potential plane-wave (PP-PW) approach based on the density functional (DFT) theory, within the generalized gradient approximation (GGA). The elastic constants (C ij), Pugh`s ratio, Cauchy`s pressure and other elastic parameters are derived and analyzed using energy strain method for the first time. We have discussed the bonding nature in the light of the electronic valence charge density. Both electron and hole-like Fermi surfaces are present in the compound under study which indicate the multiple-band nature of (Na 0.25 K 0.45)Ba 3 Bi 4 O 12. The compound is indicated to be a strongly coupled superconductor which is based on the estimated e-ph coupling constant. The thermodynamic properties such as bulk modulus, Debye temperature, heat capacities and volume thermal expansion coefficient at elevated temperature and pressure are calculated and analyzed for the first time by using quasi-harmonic model. .

Journal of Scientific Research, 2013

This is the first DFT-based first-principles prediction of the detailed optical and thermodynamic... more This is the first DFT-based first-principles prediction of the detailed optical and thermodynamic properties, including Vickers hardness and Fermi surface of 211 MAX phase Ti2GeC for which superconductivity (Tc~ 9.5 K) was reported very recently. The calculated structural properties are in excellent agreement with experiments. Our results on elastic parameters indicate a slight elastic anisotropy and brittleness of the compound. The chemical bonding is seen to be a combination of covalent, ionic and metallic nature. The rather stronger covalent bonding is responsible for its high Vickers hardness of 11.6 GPa. The investigated Fermi surface is formed mainly by the low-dispersive bands, which should be responsible for the presence of superconductivity in Ti2GeC. All the optical properties are evaluated and analyzed for two different polarization directions of incident photon. The temperature and pressure dependence of primitive cell volume, thermal expansion coefficient, specific heat...

Physica B: Condensed Matter, 2012

The structural parameters with stability upon Si incorporation and elastic, electronic, thermodyn... more The structural parameters with stability upon Si incorporation and elastic, electronic, thermodynamic and optical properties of Ti 3 Al 1-x Si x C 2 (0 ≤ x ≤ 1) are investigated systematically by the plane wave pseudopotential method based on the density functional theory (DFT). The increase of some elastic parameters with increasing Si-content renders the alloys to possess higher compressive and tensile strength. The Vickers hardness value obtained with the help of Mulliken population analysis increases as x is increased from 0 to 1. The solid solutions considered are all metallic with valence and conduction bands, which have a mainly Ti 3d character, crossing the Fermi level. The temperature and pressure dependences of bulk modulus, normalized volume, specific heats, thermal expansion coefficient, and Debye temperature are all obtained through the quasi-harmonic Debye model with phononic effects for T = 0−1000 K and P = 0−50 GPa. The obtained results are compared with other results where available. Further an analysis of optical functions for two polarization vectors reveals that the reflectivity is high in the visible-ultraviolet region up to ~10.5 eV region showing promise as good coating material.

Computational Materials Science, 2012

An investigation of U 2 Ti, a potentially safe and heavy metal-based storage material for radioac... more An investigation of U 2 Ti, a potentially safe and heavy metal-based storage material for radioactive tritium for fusion reactor, has been performed using pseudopotential density functional theory. The analysis of the elastic constants and other moduli calculated for the first time shows large anisotropy on elasticity and brittle behavior. A quasi-harmonic Debye model, which considers the vibrational contribution to the total free energy of the system, has been used to investigate the finite-temperature and finite-pressure thermodynamic properties of U 2 Ti. The electronic band structure reveals metallic conductivity and the major contribution comes from U-5f states. By analyzing the optical spectra, the origin of the various structures is also explained in terms of the calculated electronic structure. Further the reflectivity spectrum shows that the material is perfect reflector within the energy range 8-12.5 eV.

arXiv: Superconductivity, Oct 27, 2009

Two possible phases of superhard material BC 3 originating from the cubic diamond structure are i... more Two possible phases of superhard material BC 3 originating from the cubic diamond structure are investigated by ab initio pseudopotential density functional method using generalized gradient approximation (GGA). We calculate their elastic constants, electronic band structure, and density of states (DOS). Full phonon frequencies, electron-phonon coupling constant and possible superconducting T c of the metallic phase with tetragonal symmetry (t-BC 3 , space group P-42m) have for the first time been investigated at 5 and 10 GPa. The calculated electron-phonon coupling (0.67) and the logarithmically-averaged frequency (862 cm-1) show superconductivity for the undoped t-BC 3 with T c = 20 K at 5 GPa, which decreases to 17.5 K at 10 GPa.

Physica C: Superconductivity, 2007

The hexagonal AgB 2 , a hole doped system, is a potential candidate for high-T c superconductor i... more The hexagonal AgB 2 , a hole doped system, is a potential candidate for high-T c superconductor in accordance with theoretical studies. The recent observation of the onset of the superconductivity at 7.4 K is lower than the theoretically calculated value of T c. The reason for the discrepancy and the role of enhanced spin fluctuation (magnons) on the critical temperature are studied in the present paper.