EPW Forum

Dear Prof.

I calculated the phonon linewidth under different temperatures and find ther are almost the same (300K and 1200K).
The electron linewidth decease with the temprature. From the theory, based on my understanding, phonon linewidth should be a function of phonon frequency and temperature. Why it is not change?
Are there parameters I set wrong?

Best regards,
Yi-Ming

Below are the input parameters:
(Version EPW 5.4.1)
epw1.in
--
&inputepw
prefix = 'AAA'
amass(1) = ****
amass(2) = ****
outdir = './tmp/'

iverbosity = 0

elph = .true.
epwwrite = .true.
epwread = .false.

asr_typ = 'simple'

nbndsub = 10
bands_skipped = 'exclude_bands=1-58,69-80'
wannierize = .true.
proj(1) = '***'
wdata(1) = 'bands_plot = .true.'
wdata(2) = 'begin kpoint_path'
wdata(3) = 'G 0.00000 0.00000 0.00000 M 0.50000 0.00000 0.00000'
wdata(4) = 'M 0.50000 0.00000 0.00000 K 0.33333 0.33333 0.00000'
wdata(5) = 'K 0.33333 0.33333 0.00000 G 0.00000 0.00000 0.00000'
wdata(6) = 'end kpoint_path'
wdata(7) = 'bands_plot_format = gnuplot'
wdata(8) = 'use_ws_distance = .true.'
wdata(9) = 'dis_mix_ratio = 1.0'
wdata(10) = 'guiding_centres = .true.'

temps = 1200.0 ! K
dvscf_dir = 'phonon_12'
filukk = './AAA.ukk'
filkf = './kpoints.txt'
filqf = './kpoints.txt'

nk1 = 12
nk2 = 12
nk3 = 1

nq1 = 12
nq2 = 12
nq3 = 1
/

epw2.in:
--
&inputepw
prefix = 'AAA
amass(1) = *****
amass(2) = *****
outdir = './tmp/'

elph = .true.
epwwrite = .false.
epwread = .true.

asr_typ = 'simple'

nbndsub = 10
bands_skipped = 'exclude_bands=1-58,69-80'
wannierize = .false.

phonselfen = .true.
delta_approx= .true.

fsthick = 2.0 ! eV
temps = 1200.0 ! K
degaussw = 0.05 ! eV

dvscf_dir = 'phonon_12'
filukk = './AAA.ukk'
filkf = './kpoints.txt'
filqf = './kpoints-bte.txt'

nk1 = 12
nk2 = 12
nk3 = 1

nq1 = 12
nq2 = 12
nq3 = 1
/

Dear Yi-Ming,

EPW code calculates the electron and phonon linewidths by using the Eqs. (8)-(9) in the paper S. Ponce et al., Comput. Phys. Commun. 209, 116 (2016). As the equations show, the electron linewidth seems sensitive to temperature because it has the Bose distribution. The phonon linewidth is not always sensitive to temperature because the phonon linewidth only has the Fermi distribution in the formula. The temperature effect should depend on whether your target material is a metal or an insulator. Please try with much lower/higher temperatures to check the difference if you have not tried. As you know, the phonon linewidth which EPW calculates does not include the contribution of phonon-phonon scattering.

Note that the subroutine for self-energy differs from the transport subroutine. When calculating the transport properties, the code calculates the Fermi level for each temperature and then uses it. In contrast, the code uses the same Fermi energy fixed against temperature for calculating the self-energy. The Fermi energy used for self-energy is calculated using gaussian smearing when efermi_read is false, but the input value of fermi_energy is used when efermi_read is true. If you want to account for temperature variations in Fermi energy, manually change "fermi_energy" with efermi_read = true and run the EPW code for each temperature.

Best regards,
Hitoshi

Hi Yi-Ming,

I see that the same temperature ("temps = 1200.0 ! K") for both of your inputs. Can you make sure you have two different temperatures in your inputs?

Thanks,
Gyanu