Dear EPW developers,

Does EPW (qe-6.4.1) work well with the PBE functional? When I solve the anisotropic Eliashberg equations for MgB2 and other compounds with PBE norm-conserving PPs, several strange problems are encoutered. And I need your help.

For PZ-vbc-PPs, these problems are rarely encountered and the results for MgB2 seems right, so I believe that the code is properly compiled. Here are the problems.

1. For MgB2, the gap associated with sigma bands is split into two gaps at a relatively high temperature, e.g. 38 K.

Is this a normal case? How to understand this behavior?

2. When PBE is used, crash of the code is continual at the Pade continuation step. For example at 30 K, I notice that pade_aniso_gap0_030.00 file is successfully generated, but the qdos_030.00 file is not given.

Typical errors are as follows.

---------------------------tail of the output file of epw.x------------------------------

iter = 69 relerr = 2.2832899128E-04 abserr = 3.5704293835E-07 Znormi(1) = 2.1435405695E+00 Deltai(1) = 7.4248849307E-03

iter = 70 relerr = 1.9834546135E-04 abserr = 3.1021858029E-07 Znormi(1) = 2.1435269856E+00 Deltai(1) = 7.4262663069E-03

iter = 71 relerr = 4.2377705389E-04 abserr = 6.6251996642E-07 Znormi(1) = 2.1435594451E+00 Deltai(1) = 7.4231730147E-03

iter = 72 relerr = 7.7563511064E-05 abserr = 1.2125099459E-07 Znormi(1) = 2.1435641308E+00 Deltai(1) = 7.4226429720E-03

Convergence was reached in nsiter = 72

iaxis_imag : 5508.83s CPU 5630.82s WALL ( 9 calls)

Pade approximant of anisotropic Eliashberg equations from imaginary-axis to real-axis

Cutoff frequency wscut = 1.4000

pade = 26 error = 2.4469808354E+00 Re[Znorm(1)] = 2.2368031542E+00 Re[Delta(1)] = 5.5776084906E-03

-----------------------------error message-----------------------------------------

forrtl: severe (174): SIGSEGV, segmentation fault occurred

Image PC Routine Line Source

epw.x 0000000000E3BAC6 Unknown Unknown Unknown

libpthread-2.12.s 000000392220F710 Unknown Unknown Unknown

libmpi.so.12.1.0 00002B88AFE2BF32 _int_free Unknown Unknown

libmpi.so.12.1.0 00002B88AFE2AEDA free Unknown Unknown

epw.x 0000000000E7C4C3 Unknown Unknown Unknown

epw.x 00000000005395A8 io_eliashberg_mp_ 2142 io_eliashberg.f90

epw.x 0000000000539CAD io_eliashberg_mp_ 330 io_eliashberg.f90

epw.x 00000000005176EB superconductivity 934 superconductivity_aniso.f90

epw.x 000000000050F111 superconductivity 142 superconductivity_aniso.f90

epw.x 000000000044514F eliashberg_eqs_ 68 eliashberg.f90

epw.x 0000000000440B37 MAIN__ 170 epw.f90

epw.x 000000000043FFDE Unknown Unknown Unknown

libc-2.12.so 0000003921A1ED1D __libc_start_main Unknown Unknown

epw.x 000000000043FEE9 Unknown Unknown Unknown

3. When I increase the mu* to 0.21 for MgB2, the code does nothing when the convergence is achieved at the first temperature (e.g. 30 K).

Here is the tail for the output file of epw.x.

---------------------------tail of the output file of epw.x------------------------------

iter = 76 relerr = 4.2297488522E-04 abserr = 4.5806546062E-07 Znormi(1) = 1.6637843476E+00 Deltai(1) = 2.9060303329E-03

iter = 77 relerr = 5.8792876309E-04 abserr = 6.3707869487E-07 Znormi(1) = 1.6637763992E+00 Deltai(1) = 2.9077880463E-03

iter = 78 relerr = 7.7655326982E-04 abserr = 8.4212587310E-07 Znormi(1) = 1.6637644665E+00 Deltai(1) = 2.9099270456E-03

iter = 79 relerr = 8.4205214787E-04 abserr = 9.1392508655E-07 Znormi(1) = 1.6637538512E+00 Deltai(1) = 2.9120158863E-03

iter = 80 relerr = 4.6293907364E-05 abserr = 5.0247037292E-08 Znormi(1) = 1.6637516945E+00 Deltai(1) = 2.9123917895E-03

-----------------------------error message-----------------------------------------

forrtl: severe (174): SIGSEGV, segmentation fault occurred

Image PC Routine Line Source

epw.x 0000000000E3BAC6 Unknown Unknown Unknown

libpthread-2.12.s 000000392220F710 Unknown Unknown Unknown

libmpi.so.12.1.0 00002AC3D5270E4B free Unknown Unknown

epw.x 0000000000E7C4C3 Unknown Unknown Unknown

epw.x 00000000005395A8 io_eliashberg_mp_ 2142 io_eliashberg.f90

epw.x 0000000000538456 io_eliashberg_mp_ 221 io_eliashberg.f90

epw.x 0000000000512CE8 superconductivity 452 superconductivity_aniso.f90

epw.x 000000000050E83C superconductivity 89 superconductivity_aniso.f90

epw.x 000000000044514F eliashberg_eqs_ 68 eliashberg.f90

epw.x 0000000000440B37 MAIN__ 170 epw.f90

epw.x 000000000043FFDE Unknown Unknown Unknown

libc-2.12.so 0000003921A1ED1D __libc_start_main Unknown Unknown

epw.x 000000000043FEE9 Unknown Unknown Unknown

-------------------------------------------------------------------------------------------

Are the last two problems closely related to the Pade continuation? Is it helpful by seting lacon to .true.?

Look forward to your reply and thanks for your kind help!

Best wishes

Miao Gao

Ningbo University