Dear Vivek,
> Can you please provide any useful reference for the Bethe-Salpeter approach > to obtain accurate absorption spectra for solids? You can start from this reference: G. Onida, L. Reining, A. Rubio, "Electronic excitations: density-functional versus many-body Green's-function approaches", Rev. Mod. Phys. 74, 601 (2002). Greetings, 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 <[email protected]> on behalf of Vivek Christhunathan <[email protected]> Sent: Monday, February 17, 2020 1:20:21 PM To: Quantum ESPRESSO users Forum Subject: Re: [QE-users] Reg- Absorption spectrum using TDDFPT (turbo_davidson.x, turbo_lanczos.x and epsilon.x) Dear Iurii, Many thanks for your prompt reply and for your clear explanation about the related questions. I will try my calculation as per your technical comments and I will let you know here. Can you please provide any useful reference for the Bethe-Salpeter approach to obtain accurate absorption spectra for solids? Kind Regards, Vivek C __________________________________ Vivek Christhunathan PhD researcher Mechanical Engineering College of Engineering and Informatics Room 2053 Alice Perry Engineering Building National University of Ireland Galway Ireland E-mail: [email protected]<mailto:[email protected]> Phone: +353 899811181, +91 9600752742 [https://docs.google.com/uc?export=download&id=1oPtxd7PT5ljQRnuP-Gdf5upjiKPXk7Fz&revid=0B_S3ZLbRRu26NW1YallITFk1ZHMxaStQaUVoMjZ4M2NqcC9BPQ] On Fri, Feb 14, 2020 at 12:11 PM Timrov Iurii <[email protected]<mailto:[email protected]>> wrote: Dear Vivek, In order to obtain accurate absorption spectra for solids, the Bethe-Salpeter approach is the right way to go. Nonetheless, please see my comments below. epsilon.x is based on DFT and it is the code to compute absorption spectra in the independent-particle approximation, while turbo_lanczos.x and turbo_davidson.x are based on time-dependent DFT (TDDFT) and include interaction effects into account (it is possible to disable interactions and obtain the same results as epsilon.x). Moreover, in epsilon.x the intensities are not fully correct, because there is a missing term in the commutator [V,r] (a contribution from the nonlocal part of the pseudo-potential is missing, while in TDDFT codes above it is included). Technical comments: you use a hybrid functional (input_dft = 'pbe0'), therefore you should use d0psi_rs = .true. in turbo_lanczos.x and turbo_davidson.x in order to have the correct intensities in the absorption spectrum (this is true for molecules, while in solids it does not help). > ATOMIC_SPECIES > Ti 47.867 Ti.upf > O 16.00 O.upf Check this page for pseudos: https://www.materialscloud.org/discover/sssp/table/efficiency Greetings, 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 <[email protected]<mailto:[email protected]>> on behalf of Vivek Christhunathan <[email protected]<mailto:[email protected]>> Sent: Friday, February 14, 2020 12:24:25 PM To: [email protected]<mailto:[email protected]> Subject: [QE-users] Reg- Absorption spectrum using TDDFPT (turbo_davidson.x, turbo_lanczos.x and epsilon.x) Dear QE users, Greetings!!! I am trying to find the absorption spectrum for the material 'TiO2' supercell (2*1*1) which consists of 24 atoms. I tried a lot to find the absorption spectrum by reading all the related threads from QE. I have tried with all the methods such as turbo_davidson.x, turbo_lanczos.x and epsilon.x. I can only succeed with the use of epsilon.x but I am unable to get the same results for the turbo_davidson.x and turbo_lanczos.x. I would like to know the reason behind this. And secondly to find an absorption spectrum of the material does epsilon.x method gives accurate results when compared with the other two? Thirdly I have tried it for the Zn doped TiO2 supercell. This time all the methods did not give a hand for my calculation. The input files are given below. I would be very grateful if you help me out in this regard. Please let me know if you need any further information. Looking forward to hearing from you. Thanks in advance. # self-consistent calculation &control calculation = 'scf' prefix = 'TiO2' pseudo_dir = './' outdir = './outTiO2' !etot_conv_thr = 1e-5 forc_conv_thr = 1e-4 / &system ibrav = 0 celldm(1) = 14.113 nat = 24 ntyp = 2 ecutwfc = 80.0 ecutrho = 800 nbnd = 300 input_dft = 'pbe0' / &electrons mixing_beta=0.3 conv_thr = 1.0d-8 diagonalization = 'david', mixing_mode = 'plain', / &IONS / &cell / CELL_PARAMETERS (alat) 1.000927809 0.000000000 0.000000000 0.000000000 0.500440909 0.000000000 0.000000000 0.000000000 1.235414320 ATOMIC_SPECIES Ti 47.867 Ti.upf O 16.00 O.upf ATOMIC_POSITIONS (crystal) Ti 0.000000000 0.000000000 -0.000006420 Ti 0.500000000 0.000000000 -0.000006418 Ti 0.250000017 0.500000000 0.499993602 Ti 0.750000015 0.500000000 0.499993602 Ti 0.000000000 0.500000000 0.250006398 Ti 0.500000000 0.500000000 0.250006394 Ti 0.250000016 0.000000000 0.750006426 Ti 0.750000016 0.000000000 0.750006426 O 0.000000000 0.000000000 0.212511476 O 0.500000000 0.000000000 0.212511476 O 0.250000011 0.500000000 0.712511501 O 0.750000021 0.500000000 0.712511501 O 0.000000000 0.500000000 0.462514694 O 0.500000000 0.500000000 0.462514705 O 0.250000019 0.000000000 0.962514709 O 0.750000013 0.000000000 0.962514709 O 0.250000008 0.000000000 0.537488518 O 0.750000024 0.000000000 0.537488518 O 0.000000000 0.500000000 0.037488489 O 0.500000000 0.500000000 0.037488487 O 0.250000019 0.500000000 0.287485309 O 0.750000013 0.500000000 0.287485309 O 0.000000000 0.000000000 0.787485317 O 0.500000000 0.000000000 0.787485307 K_POINTS gamma # turbo_lanczos.x calculation &lr_input prefix ='TiO2' outdir ='./outTiO2' !restart_step = 100, !restart = .true. / &lr_control itermax = 500 ipol = 1 !d0psi_rs = .true. / # turbo_spectrum.x calculation &LR_INPUT prefix = 'TiO2' outdir = './outTiO2' itermax0 = 500 itermax = 10000 extrapolation = 'osc' epsil = 0.01 units = 1 start = 0.0 end = 4.0 increment = 0.01 ipol = 1 / # turbo_davidson.x calculation &lr_input prefix = 'TiO2' outdir = './outTiO2' / &lr_dav !if_dft_spectrum = .false. num_eign = 5 num_init = 10 num_basis_max = 90 residue_conv_thr = 1.0E-4 start = 0.0 finish = 3.50 step = 0.001 broadening = 0.004 reference = 0.3 / # turbo_spectrum.x calculation &lr_input prefix = 'TiO2' outdir = './outTiO2' td = 'davidson' epsil = 0.004 start = 0.0d0 end = 3.5d0 increment = 0.001d0 eign_file = 'TiO2.eigen' / Kind Regards, Vivek C __________________________________ Vivek Christhunathan PhD researcher Mechanical Engineering College of Engineering and Informatics Room 2053 Alice Perry Engineering Building National University of Ireland Galway Ireland E-mail: [email protected]<mailto:[email protected]> Phone: +353 899811181, +91 9600752742 [https://docs.google.com/uc?export=download&id=1oPtxd7PT5ljQRnuP-Gdf5upjiKPXk7Fz&revid=0B_S3ZLbRRu26NW1YallITFk1ZHMxaStQaUVoMjZ4M2NqcC9BPQ] _______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>) users mailing list [email protected]<mailto:[email protected]> https://lists.quantum-espresso.org/mailman/listinfo/users
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