Vibrational Spectroscopy
Vibrational Spectroscopy
CASTEP can compute vibrational (phonon) modes for metals and insulators using either of density functional perturbation theory (DFPT) or finite displacements in conjunction with supercells. In addition to the traditional method of a user-specified supercell (a.k.a. the "direct method") CASTEP implements a new method which automatically selects and generates a series of supercells commensurate with the desired phonon wavevector criteria. CASTEP itself contains a full-featured lattice dynamics code, which takes control of setting up the entire calculation and and no external software (such as Phonoy, PHONON, Phon) is required.
The available capabilities and features include
- DFPT
- Full BZ sampling using Fourier interpolation for DOS and dispersion.
- Finite-displacements (Supports full range of Hamiltonians including DFT+U, DFT+SO, hybrids)
- Full BZ sampling using traditional finite-displacement/spuercell method for DOS and dispersion.
- Full BZ sampling using more efficient and automated non-diagonal supercell method for DOS and dispersion.
- Acoustic sum-rule enforcement correction in either real- or reciprocal space.
- Full use of space-group symmetry to reduce redundant computation of perturbations.
- Electric field response DFPT to give IR and Raman intensities and NLO coefficients.
- Full symmetry analysis to compute irreducible representaions.
- External tools for postprocessing and plotting phonon dispersion and DOS.
- External tool for isotopic substitution calculations.
Experimental and calculated INS spectra of NaHF2
For more information on vibrational properties in CASTEP see the following talks from the 2019 Castep workshop:
- Phonons - Dr Peter Byrne (York)
- Advanced Vibrational spectroscopy methods - Dr Keith Refson (STFC / RAL)
The a-CLIMAX package by A J Ramirez-Cuesta (ISIS) for simulating INS spectra from CASTEP calculations.
Key References
- Variational density-functional perturbation theory for dielectrics and lattice dynamics K. Refson, P. R. Tulip and S. J Clark Phys. Rev. B 73, 155114 (2006)
- S. Baroni et al (2001), Rev. Mod. Phys 73, 515
- X. Gonze (1997) PRB 55 10377