|
Method
and Scope
MedeA-Phonon lets you perform calculations of lattice vibrational
spectra and derived properties for a wide range of materials including
solids, surfaces and molecules. Knowledge of the phonon dispersions
and phonon densities of states allows quantitative prediction of
materials properties such as thermodynamic functions and spectroscopic
data. Application examples are heat capacity, enthalpy, entropy
and the free energy, neutron scattering cross sections, the interpretation
of IR/Raman spectra and the prediction of phase instabilities and
phase transitions. Using MedeA-Phonon you can compute vibrational
properties for materials containing any species of atoms including
heavy metals or rare earth elements.
| Features
MedeA-Phonon, which was developed in collaboration
with Prof. K. Parlinski, employs the so-called direct approach
[1], deriving force constant matrices from forces calculated
by VASP for supercells with displaced
atoms. Features of MedeA-Phonon are:
-
Full
integration in MedeA
environment
-
Automated setup for any type of solid/surface/molecular
system
-
Uses
VASP to generate ab-initio forces
-
Uses
MedeA's powerful job server concept
-
Speeds
up calculations through parallel VASP
-
Simple
analysis and data export to Windows applications
|
|
Application
example
Starting from a structural model for AlN retrieved
from MedeA-InfoMaticA, Phonon
automates all steps needed to derive the dispersion relation
for the full Brillouin zone, the Phonon density of states
and thermodynamic functions like internal energy, entropy,
specific heat and free energy. These steps include:
- Creation of a supercell suitable for the calculation of
the interatomic forces
- Setup of displacement models needed
to calculate forces
- Symmetry analysis for displaced structure models
- Identification of Raman/IR active modes
- Computation of forces
- Construction of force constant matrix
and dynamical matrix
- Computation of phonon dispersion
relation and density of states
- Derivation of thermodynamic functions
|
|
| A 72-atom supercell
is used to calculate interatomic forces upon atomic displacements.
A symmetry analysis identifies the IR/Raman active modes. The
calculated phonon dispersion curves agree to 0.2 THz with inelastic
X-ray and neutron scattering data. Thermodynamic functions like
the entropy of the system, the heat capacity and the free energy
are readily available from the MedeA-Phonon output.
References
- 1. K. Parlinski, Z. Q. Li, Y. Kawazoe, Phys. Rev. Lett.
78, 4063 (1997)
- Inelastic X-ray scattering: M. Schwoerer-Böhning, A. T.
Macrander, M. Pabst, P. Pavone, Phys. Status Solidi (b)
215, 177 (1999)
|
|
|
