Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA first-principles approach to nonlinear lattice dynamics: Anomalous spectra in PbTe
239
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Here we introduce a new approach to compute the finite temperature lattice dynamics from first-principles via the newly developed slave mode expansion. We study PbTe where inelastic neutron scattering (INS) reveals strong signatures of nonlinearity as evidenced by anomalous features which emerge in the phonon spectra at finite temperature. Using our slave mode expansion in the classical limit, we compute the vibrational spectra and show remarkable agreement with temperature dependent INS measurements. Furthermore, we resolve experimental controversy by showing that there are no appreciable local nor global spontaneously broken symmetries at finite temperature and that the anomalous spectral features simply arise from two anharmonic interactions. Our approach should be broadly applicable across the periodic table.
rate research
Read More
We investigate the harmonic and anharmonic contributions to the phonon spectrum of lead telluride, and perform a complete characterization of how the anharmonic effects dominate the phonons in PbTe as temperature increases. This effect is the strongest factor in the favorable thermoelectric properties of PbTe: an optical-acoustic phonon band crossing reduces the speed of sound and the intrinsic thermal conductivity. We present the detailed temperature dependence of the dispersion relation and compare our calculated neutron scattering cross section with recent experimental measurements. We analyze the thermal resistivitys variation with temperature and clarify misconceptions about existing experimental literature. This quantitative prediction opens the way to phonon phase space engineering, to tailor the lifetimes of crucial heat carrying phonons.
A description of non-collinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within the optimized effective potential (OEP) framework. With the example of a magnetically frustrated Cr monolayer it is shown that the resulting magnetization density exhibits much more non-collinear structure than standard calculations. Furthermore, a time-dependent generalization of the non-collinear OEP method is well suited for an ab-initio description of spin dynamics. We also show that the magnetic moments of solids Fe, Co and Ni are well reproduced.
An accurate and easily extendable method to deal with lattice dynamics of solids is offered. It is based on first-principles molecular dynamics simulations and provides a consistent way to extract the best possible harmonic - or higher order - potential energy surface at finite temperatures. It is designed to work even for strongly anharmonic systems where the traditional quasiharmonic approximation fails. The accuracy and convergence of the method are controlled in a straightforward way. Excellent agreement of the calculated phonon dispersion relations at finite temperature with experimental results for bcc Li and bcc Zr is demonstrated.
According to Vegards law, larger radius atoms substitute for smaller atoms in a solid solution would enlarge the lattice parameters. However, by first-principles calculations, we have observed unusual lattice shrinkage when W replaces Ge in rock salt GeTe. We attribute this anomalous contract to the larger electronegativity difference between W and Te than between Ge and Te, which results in shorter W-Te bonds and pronounced local distortion around W dopants. The present work would provide new insight into the lattice parameter determination and a deeper understanding of the structural properties of ternary solid solutions.
We present a computationally efficient general first-principles based method for spin-lattice simulations for solids. Our method is based on a combination of atomistic spin dynamics and molecular dynamics, expressed through a spin-lattice Hamiltonian where the bilinear magnetic term is expanded to second order in displacement, and all parameters are computed using density functional theory. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and is seen to be in good agreement with previous simulations performed with an empirical potential approach. In addition, we also illustrate the abilities of our method on a more conceptual level, by exploring dissipation-free spin and lattice motion in small magnetic clusters (a dimer, trimer and quadmer). Our method opens the door for quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
