10.5. Phonon density of states

Instructions for computing phonons density of states (DOS) are almost identical to those of band-structure calculations. The only difference is sampling of phonons wave-vectors which is done on a grid of q-points in case of DOS calculations. One can create the following input file to perform as DOS calculation:


Please see Phonon band structure for more information regarding how dynamical matrix is calculated in nonself-consistent DFPT calculations, as well as LO-TO corrections.

info.calculationType = 'dfpt-phonon-dos'
info.savepath = './results/bn_real_phonon_dos'
dfpt.phononData = './results/bn_real_phonon.mat'
dfpt.dielectricData = './results/bn_real_dielectric.mat'
dfpt.qpointGridn = [10 10 10]
dfpt.asr = [1,1,1]

We expand on these important keywords.

  • info.calculationType is a string determining the type of the calculation;

  • info.savepath points to the file that stores the ouput data;

  • dfpt.dielectricData points to the path of the file containing the ion-clamped dielectric tensor (only required for non-metallic systems), i.e. the output of dielectric calculation. This information is used to calculate the LO-TO corrections;

  • dfpt.phononData points to the path of the file containing the dynamical matrix and Born effective charges, i.e. the output of phonon calculation; BECs are used for calculating LO-TO corrections, and dynamical matrix is used in Fourier interplation process.

  • dfpt.qpointGridn use a [10,10,10] grid to sample the Brillouin zone. The grid is forced to be \(\Gamma\)-centered.

  • dfpt.asr it is a \(1\times 3\) vector which determines the status of various acoustic sum rules in DFPT calculations. In particular, the first two entries determines if acoustic sum rule and charge neutrality will be enforced to dynamical matrix and Born effective charges, respectively. RESCU assumes that all sum rules are active by default.

Then execute RESCU as follows

rescu -i bn_real_phonon_dos

Upon completion, RESCU will write the DOS data in DensityOfStates.txt. Additional data is found in the dfpt and dos structure stored in ./results/bn_real_phonon_dos.mat.

>> load results/bn_real_phonon_dos.mat
>> dfpt

dfpt =

  struct with fields:

             IFC: [6x6x27 double]
             asr: [1 1 1]
            desc: [1x1 struct]
          dynMat: [6x6x1000 double]
      phononFreq: [6x1000 double]
      phononMode: {1000x1 cell}
    qpointDirect: [1000x3 double]
     qpointGridn: [10 10 10]
            type: 'phonon-dos'

>> dos

dos =

  struct with fields:

      desc: [1x1 struct]
    dosvec: [6024x1 double]
    nrgvec: [6024x1 double]

Please see Phonon band structure for further description of important variables. You may then plot the phonon DOS using RESCU’s plotting tool

rescu -p ./results/bn_real_phonon_dos.mat

RESCU will display a plot of the phonon DOS, shown in Fig. 10.5.1 and also save the figure to bn_real_phonon_dos_plot.fig.

Boron nitride phonon DOS

Fig. 10.5.1 Boron nitride phonon DOS