Ads: Get Admission into 200 Level and Study any Course in any University of Your Choice. Low Fees | No JAMB UTME. Call 09038456231

Calculations of Phonons and Phonon Dispersion in Lifep Pnictide Superconductor

ADS! Obtain Up to N300,000 Cash in the 2020 Aspire Contest

Calculations of Phonons and Phonon Dispersion in Lifep Pnictide Superconductor.

ABSTRACT

Not too long ago(2008),a new pnictide Superconductor free from arsenic was discovered –LiFeP. It belongs to the family of the so called ‘111’ type iron Superconductor.

It has unique characteristics in its normal state which can be useful in understanding the unusual high temperature superconductivity observed in iron pnictide compounds.

In this work,we studied LiFeP from first principles. The structure was optimised,electronic structure calculations were performed yielding lattice constants that differed only 2 − 9% from experiment.

Band structure was calculated and electronic density of states showing no band gap was found. Calculations on phonon modes was also done.

From observing the phonon normal modes,the FeP plane was found to be largely decoupled from the Li atoms.

In some modes the P is also decoupled from the Fe plane.A small band gap of about 25cm1 (≡ 35)K was also noticed in the phonon band structure

TABLE OF CONTENTS

1.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Phonons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Superconductivity . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.3 BCS theory of superconductivity and high Tc superconductors . 2
1.1.4 Pnictide superconductors . . . . . . . . . . . . . . . . . . . . . 3
2.1 The Hamiltonian of a solid . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Splitting the Hamiltonian . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 The electronic Hamiltonian . . . . . . . . . . . . . . . . . . . . 7
2.1.3 Density Functional Theory: The Hohenberg and Kohn Theorem 9
2.1.4 The Energy Functional . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.5 Local density Approximation . . . . . . . . . . . . . . . . . . . 11
2.1.6 The generalized Gradient Approximation . . . . . . . . . . . . . 12
2.1.7 Plane waves pseudo potentials . . . . . . . . . . . . . . . . . . . 13
2.1.8 Density of states . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.9 The PWSCF program . . . . . . . . . . . . . . . . . . . . . . . 14
3.1 Details of Computation . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2 Results:Electronic properties . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1 Phonons calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.1 Normal vibrational modes . . . . . . . . . . . . . . . . . . . . . 23
4.2 Inter atomic force constants . . . . . . . . . . . . . . . . . . . . . . . . 24
4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5 Conclusion 46

INTRODUCTION

1.1 Phonons

Energy is involved in the collective motion of atoms in a material: the atoms vibrate together. This energy occurs in ‘packets’called phonons. In other words the energy is quantized and a phonon is a quantum of such energy.

One can also view phonons as a quasi particles which carry the energies of collective vibrations of atoms(much in the same way as the more familiar photons [1] that are also quasi particles which carry electromagnetic energy).

Phonons are connected with many properties of materials e.g thermal conductivity-when a solid is heated,its atoms vibrate meaning phonons are being created/destroyed and scattered.

Phonons also play an important role in elec- trical conductivity since the electrons in solids can be scattered [2] by phonons con- sequently decreasing the electrical conductivity of the material.

A strange situation has,however,been found in nature, certain materials demonstrate infinite conductiv- ity;the electrons move without scattering off of phonons despite existence of phonons in such materials.This property of such materials is called superconductivity.

1.2 Superconductivity

It was discovered in 1911 by the Dutch physicist Karmmerlingh Onnes in the course of his experiment on electrical conductivity of metals at low [3] temperature.

It is the complete loss of electrical resistivity;the substance exhibits perfect electrical conductiv- ity.It is also accompanied by expulsion of an applied magnetic field from the material.

BIBLIOGRAPHY

C.Kittel,Introduction to Solid State physics,7th ed.(Wiley,New York,1996)

H.Hameka,Advanced Quantum Chemistry (Addison-Wesley,Reading,MA,1955)

M.Croyt,D.Pavuna,Introduction to Superconctivity and high Tc material(World Scientific,Singapore,1992)

J.Bardeen,L.Cooper and J.Schrieffer, Phys. Rev.Lett.,108 (1957)1175

Y.Kamihara, T.Wantanbe, M.Hirano and H.Hosono Chem. Soc.,130(2008)3296

Y.Kamihara, H.Hiramatsu, M.Hirano, R.Yanaji Chem soc.,126(2006)10012

Enter your email address:

Delivered by TMLT NIGERIA

Join Over 3,500 000+ Readers Online Now!


=> FOLLOW US ON INSTAGRAM | FACEBOOK & TWITTER FOR LATEST UPDATES

ADS: KNOCK-OFF DIABETES IN JUST 60 DAYS! - ORDER YOURS HERE

COPYRIGHT WARNING! Contents on this website may not be republished, reproduced, redistributed either in whole or in part without due permission or acknowledgement. All contents are protected by DMCA.
The content on this site is posted with good intentions. If you own this content & believe your copyright was violated or infringed, make sure you contact us at [[email protected]] to file a complaint and actions will be taken immediately.

Tags: , , ,

Comments are closed.