[QE-users] Absorption spectra of a bulk material

[Timrov Iurii]

Dear Vipul,


> I am using QE 6.2.1


>From your output I see that you are actually using QE 6.1... So, first of all, please let's stick to the latest version of QE, i.e. 6.4.1, as I suggested in my previous email.


> In accordance with the previous suggestions I have changed my TD file...


Great! But before performing TDDFT calculations, let's make sure that the ground-state calculation was done properly.


> I would like to mention that GGA file is converging...


Could you provide your input and output files, please? In my case I did not manage to converge the PWscf calculation with the input file which you sent in the past. Did you change something?


Do you use only k=0? Note that for bulk systems using k=0 and primitive cell is not ok. For bulk, one has either to use supercells and gamma sampling or to use primitive cells and appropriately dense k-points sampling.


If you want to compute an absorption spectrum of solids, TDDFT with local exchange-correlation kernels (like TDLDA or TDGGA) is not a good choice. You should resort e.g. to GW+BSE. For that, you may try to use e.g. the Yambo code.


HTH


Regards,

Iurii


--
Dr. Iurii Timrov
Postdoctoral Researcher
STI - IMX - THEOS and NCCR - MARVEL
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Vipul Shivaji Ghemud <vipul at physics.unipune.ac.in>
Sent: Thursday, May 23, 2019 8:14:26 AM
To: users at lists.quantum-espresso.org
Subject: Re: [QE-users] Absorption spectra of a bulk material

Dear Iurii,
In accordance with the previous suggestions I have changed my TD file but
still facing same problem. TD file is as below:

&lr_input
    prefix = 'cfts'
    outdir = './out1'
    restart = .false.
/
&lr_dav
    num_eign = 10,
    num_init = 20,
    num_basis_max = 80,
    residue_conv_thr = 1.0D-4,
    start  = 0.0,
    finish = 1.5,
    step   = 2.0D-4,
    broadening = 0.005,
    reference = 0.5,
    p_nbnd_occ  = 4,
    p_nbnd_virt = 15,
    poor_of_ram  = .false.
    poor_of_ram2 = .false.
/

##########################################################################

I would like to mention that GGA file is converging but not giving any
band gap (it is showing band crossing), so it'll not show any absorption
coefficient. I am using QE 6.2.1 for HSE calculations, and they are
converging very well, still i am getting following output:



     Program turboTDDFT v.6.1 (svn rev. 13369) starts on 21May2019 at
17:27:29

     This program is part of the open-source Quantum ESPRESSO suite
     for quantum simulation of materials; please cite
         "P. Giannozzi et al., J. Phys.:Condens. Matter 21 395502 (2009);
          URL http://www.quantum-espresso.org",
     in publications or presentations arising from this work. More details at
     http://www.quantum-espresso.org/quote

     Parallel version (MPI), running on    56 processors
     R & G space division:  proc/nbgrp/npool/nimage =      56

     Reading data from directory:
     ./out1/cfts.save

   Info: using nr1, nr2, nr3 values from input

   Info: using nr1, nr2, nr3 values from input

############################################################################


> Dear Vipul,
>
>
> I run your test using QE 6.4.1 on my workstation with 8 cores. In the
GGA > case, the
> PWscf calculation did not converge after 100 iterations - so this is the
> first
> problem which you should solve before performing any linear-response
> calculation
> using the TDDFPT component of QE. In the case of hybrids (i.e. HSE)
please > make sure
> as well that the PWscf calculation converges with a required precision.
>
>
> Concerning your input for the turbo_davidson.x code: please see example
> TDDFPT/examples/example08 and read carefully the documentation in
> TDDFPT/Doc. There
> is no need to run turbo_spectrum.x after turbo_davidson.x (it is useful
> only in
> certain cases: see TDDFPT/examples/example08/run_example).
>
>
> HTH
>
>
> Regards,
>
> Iurii
>
>
> --
> Dr. Iurii Timrov
> Postdoctoral Researcher
> STI - IMX - THEOS and NCCR - MARVEL
> Swiss Federal Institute of Technology Lausanne (EPFL)
> CH-1015 Lausanne, Switzerland
> +41 21 69 34 881
> http://people.epfl.ch/265334

--
Vipul S. Ghemud
Ph.D. student.
Dept of Physics,
SPPU, Ganeshkhind,
Pune- 411007.

_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>)
users mailing list users at lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20190523/98ef02d9/attachment.html>