Dear abinit users,

I am trying to calculate the Tc of PbTaSe2, which is experimentally around 3.8K. But, when I try to calculate it, my value is nearly ten times smaller!

Here is my groundstate input file and anaddb file. Any help is greatly appreciated!

ndtset 32

pawxcdev 0

#

# DATASET 1 : make ground state wavefunctions and density

#

tolwfr1 1.0d-14

nline1 8 # This is to expedite the convergence of higher-lying bands

rfphon1 0 # for DS1 do _not_ do perturbation

nqpt1 0 # for DS1 do _not_ do perturbation

prtwf1 1 # need GS wavefunctions for further runs

getwfk1 0

kptopt1 3

# enforce calculation of forces at each SCF step

optforces 1

qpt2 0.00000000E+00 0.00000000E+00 0.00000000E+00

qpt3 1.66666667E-01 0.00000000E+00 0.00000000E+00

qpt4 3.33333333E-01 0.00000000E+00 0.00000000E+00

qpt5 5.00000000E-01 0.00000000E+00 0.00000000E+00

qpt6 3.33333333E-01 1.66666667E-01 0.00000000E+00

qpt7 5.00000000E-01 1.66666667E-01 0.00000000E+00

qpt8 -3.33333333E-01 3.33333333E-01 0.00000000E+00

qpt9 0.00000000E+00 0.00000000E+00 5.00000000E-01

qpt10 1.66666667E-01 0.00000000E+00 5.00000000E-01

qpt11 3.33333333E-01 0.00000000E+00 5.00000000E-01

qpt12 5.00000000E-01 0.00000000E+00 5.00000000E-01

qpt13 3.33333333E-01 1.66666667E-01 5.00000000E-01

qpt14 5.00000000E-01 1.66666667E-01 5.00000000E-01

qpt15 -3.33333333E-01 3.33333333E-01 5.00000000E-01

#

# DS5 get DDK perturbation (stored in GKK matrix element files)

#

tolwfr16 1.0d-14

qpt16 0.0 0.0 0.0

rfphon16 0

rfelfd16 2

prtwf16 0

# WF on full BZ

tolwfr17 1.0d-14

prtwf17 1

getwfk17 1

nstep17 1

nline17 1

nqpt17 0

rfphon17 0

# Compute the GKK correctly (no gauge problem)

# This step is very quick as NSCF+nstep 1

qpt18 0.0 0.0 0.0

prtgkk18 1 # print out gkk files directly

iscf18 -2

tolwfr18 1.0d-14

nstep18 1

nline18 1

getwfk18 17

get1den18 2

#continue for other qpoints

# DS12 get the ddk matrix elements on the full grid

prtgkk32 1

rfphon32 0 # no phonons here

rfelfd32 2 # Activate the calculation of the d/dk perturbation

qpt32 0.0 0.0 0.0 # This is a calculation at the Gamma point

iscf32 -3 # The d/dk perturbation must be treated non SC-ly

tolwfr32 1.0d-14 # Must use tolwfr for non-self-consistent calculations

nstep32 1

nline32 1

getwfk32 17

get1den32 5

#

# general data for all phonon calculations:

#

prepgkk 1 # flag to calculate all perturbations for el-phon calculations

use_nonscf_gkk 0 # enforce old default and scf-calculate all perturbations

nqpt 1 # 1 qpoint at a time

tolvrs 1.e-8 # tolerance on 2DTE convergence: potential^(1) is what we need

getwfk 1 # all other DS get wf from DS1

prtwf 0

rfatpol 1 4 # all atoms are perturbed

rfdir 1 1 1 # all directions of perturbation

rfphon 1

#

# Common data for GS and perturbation runs

#

# The kpoint grid is minimalistic to keep the calculation manageable.

ngkpt 12 12 4

kptopt 3

# As the kinetic energy cutoff

ecut 33

pawecutdg 66

pawovlp -1

# Use a centered grid for the kpoints

nshiftk 1

shiftk 0.0 0.0 0.0

#

# Common data

#

acell 6.5755478745E+00 6.5755478745E+00 1.8026772888E+01

rprim

0.5 sqrt(3/4) 0

-0.5 sqrt(3/4) 0

0 0 1

nband 20

# include metallic occupation function with a small smearing

occopt 7

tsmear 0.001

natom 4

typat 3 1 3 2

xred 2/3 2/3 5/6

2/3 2/3 1/2

2/3 2/3 1/6

1 1 0

nstep 800

ntypat 3

znucl 82 73 34

anaddb file:

# turn on calculation of the electron-phonon quantities

elphflag 1

telphint 0

kptrlatt 12 0 0 0 12 0 0 0 4

elphsmear 0.01

# Path in reciprocal space along which the phonon linewidths

# and band structure will be calculated

nqpath 7

qpath

0.0 0.0 0.0

2/3 1/3 0.0

1/2 0.0 0.0

0.0 0.0 0.0

2/3 1/3 1/2

1/2 0.0 1/2

0.0 0.0 1/2

# Coulomb pseudopotential parameter

mustar 0.1

# Minimalistic qpoint grid

ngqpt 6 6 2

# impose acoustic sum rule in a symmetric way

asr 2

dipdip 1

chneut 0

# bravais lattice necessary

brav 1

# qpt grid

nqshft 1

q1shft 0.0 0.0 0.0

#

ifcflag 1

ifcana 1

ifcout 0

# ifc for all atoms?

natifc 0

atifc 1 2 3

# print dielectric matrix with freq dependence

dieflag 0

# print out eigenvectors and symmetrize dyn matrix

eivec 1

#Wavevector list number 1 (Reduced coordinates and normalization factor)

nph1l 1

qph1l

0.00000000E+00 0.00000000E+00 0.00000000E+00 1

## Lambda and Tc values are too small

### Re: Lambda and Tc values are too small

Hello,

we have seen similar effects with some compounds. I think it is due to a rough interpolation of the EPC at low q and omega, which makes the a2F function too large at low w. This unbalances the calculation of omega_log, which is the large lambda limiting maximal value of Tc.

Could you post omega_log, the a2F function, lambda values, and test with different Gaussian smearings as well as the tetrahedron integration?

we have seen similar effects with some compounds. I think it is due to a rough interpolation of the EPC at low q and omega, which makes the a2F function too large at low w. This unbalances the calculation of omega_log, which is the large lambda limiting maximal value of Tc.

Could you post omega_log, the a2F function, lambda values, and test with different Gaussian smearings as well as the tetrahedron integration?

Matthieu Verstraete

University of Liege, Belgium

University of Liege, Belgium

### Re: Lambda and Tc values are too small

Also, 12 12 4 is a bit coarse. Even if your system has a large unit cell, unfortunately, the k grid convergence can be quite slow

Matthieu Verstraete

University of Liege, Belgium

University of Liege, Belgium