Vibrational spectra and phonon dispersion relations

IR and Raman vibrational spectra (phonon eigenfrequences at Gamma point) are calculated either using classical lattice dynamics approach (GULP program), or for smaller periodic system using ab initio quantum mechanical approach within Density Functional Theory framework (Crystal, VASP). Vizualitations and animations are prepared using JMol package.

Phonon dispersion relations are calculated using VASP combined with Phonopy program. Some example results are presented below.

Na-SOD FIR spectra: comparison with experiment

Na-LTA FIR spectra: comparison with experiment

Fig. 1. Na-SOD (left) and Na-LTA (right) far IR spectra: comparison with experiment [1,2].

Fig. 2. Visualization of selected normal modes of vibration: Na-LTA (left), carbon clathrate Mg₈C₄₆ (right) [3,4].

Fig. 3. Decomposed FIR spectra of Mg₂Si (left) and Mg₂Si_0.98Bi_0.02 (right) [5].

Table 1. Calculated and measured positions of selected bands in FIR spectra of bismuth doped Mg₂Si [5].

Ab initio calculations (cm^-1)
Mg₂Si			294
Mg₆₄Si₃₁Bi	267	278	292	313	326	342
Mg₆₃BiSi₃₂	263				329	341
Mg₆₄Si₃₂Bi		284			328
Experimental results (cm^-1)
Mg₂Si	266		291	315	326	338
Mg₆₄Si_31.8Bi_0.16	266	284	291	314	326	337
Mg₆₄Si_31.68Bi_0.32	266	280	292	314	326	339
Mg₆₄Si_31.52Bi_0.48	265	280	293	318	327	338
Mg₆₄Si_31.36Bi_0.64	266	280	291	314	326	338