Search found 26 matches

by jerkov
Fri Jun 26, 2020 12:01 am
Forum: Response calculations
Topic: Electron-phonon coupling (EPC)
Replies: 2
Views: 160

Re: Electron-phonon coupling (EPC)

Hi Dr. Matteo, Thanks for the thorough response. I checked out "The Abinit Project: Impact, environmen, and recent developments." From the description in Sect 3.3, it sounds like Abinit already does what I want: "To address these limitations, abinit v8 provides a new driver explicitly designed to co...
by jerkov
Thu Jun 25, 2020 11:36 pm
Forum: Input file
Topic: elasto-optic coefficients
Replies: 4
Views: 1691

Re: elasto-optic coefficients

Hi Professor Zwanziger or whoever it may concern, I've followed your method to obtain the photoelastic constants, p_ijkl. However, I'm wondering if these are the same thing as the elasto-optic coefficients that go into the expression for the piezoelectric contribution to the Pockels tensor, appearin...
by jerkov
Thu Jun 18, 2020 4:29 pm
Forum: Response calculations
Topic: Electron-phonon coupling (EPC)
Replies: 2
Views: 160

Electron-phonon coupling (EPC)

Hi all, I'm confused on where to start on an electron-phonon coupling (EPC) calculation. I'm working with a semiconductor, so it seems like the tutorial Eph (https://docs.abinit.org/tutorial/eph/) is not well suited for my problem. Also, this tutorial calculates the Eliashberg function (alpha^2F and...
by jerkov
Thu Jun 18, 2020 3:16 pm
Forum: Post-processing Tools
Topic: Axes used in dielectric tensor [SOLVED]
Replies: 2
Views: 230

Re: Axes used in dielectric tensor [SOLVED]

Hi Eric,

That makes sense, thanks a bunch!

J
by jerkov
Wed Jun 17, 2020 2:56 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi everyone,

The issue is resolved. I used more qpts (effectively a 3x3x3 supercell), and the instability disappeared. Thanks for all the help!

J
by jerkov
Sat Jun 13, 2020 12:50 am
Forum: Response calculations
Topic: Units of NLO Calculations
Replies: 0
Views: 433

Units of NLO Calculations

Hi all, I'm confused about the units of various values in my NLO anaddb output file. What are the units of Raman susceptibility? From the accompanying paper (10.1103/PhysRevB.71.125107) eqn. 28 suggests it would be something like bohr^(3/2), but that seems to contradict the Raman polarizability's us...
by jerkov
Tue Jun 09, 2020 4:41 pm
Forum: Input file
Topic: Non primitive cells, space groups [SOLVED]
Replies: 3
Views: 215

Re: Non primitive cells, space groups [SOLVED]

Hi Eric, Thanks for the suggestions. I confirmed the cell was Amm2 with a separate software, and I also made sense of the symrel printed by Abinit. As I said earlier, I only expected to see 4 matrices, not 8 as I do in the log file. However, each one is a duplicate, so there are only 4 different mat...
by jerkov
Thu Jun 04, 2020 6:35 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Eric, I believe I imposed ASR. The Gamma point itself is stable, but not wavevectors near it. Here's my anaddb input file: !Input file for the anaddb code. Analysis of the SiO2 DDB !Flags dieflag 1 ! Frequency-dependent Dielectric tensor flag ifcflag 1 ! Interatomic force constant flag thmflag 1 ...
by jerkov
Thu Jun 04, 2020 6:08 pm
Forum: Input file
Topic: Non primitive cells, space groups [SOLVED]
Replies: 3
Views: 215

Non primitive cells, space groups [SOLVED]

Hi all, I am working with a cell that can either be expressed as primitive, monoclinic Pm or non-primitive (2 formula units), orthorhmobic Amm2. I want to use the larger, orthorhombic cell for a certain calculation, specifically because it has orthogonal lattice vectors. To allow Abinit to complete ...
by jerkov
Thu May 28, 2020 9:10 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Eric and Andy and whoever else is reading, I'm working with a crystal that is stable at 0 K and with very small forces order ~1e-8 Hartree/Bohr. Yet I have a few imaginary frequencies in my BZ. 11 out of the 846 values when I choose to have nwchan = 5 and nchan = 1250 are imaginary. I was going t...
by jerkov
Tue May 12, 2020 8:57 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Great! All good then. You can mark this as solved.
by jerkov
Tue May 12, 2020 8:52 pm
Forum: Post-processing Tools
Topic: Axes used in dielectric tensor [SOLVED]
Replies: 2
Views: 230

Axes used in dielectric tensor [SOLVED]

Hi all, I am confused about what axes are used in the output dielectric, electro-optic, and piezoelectric (d tensor) tensors. I did not align my the optic axis along the z axis, and my axes are non-orthogonal. I understand that most of the well-known formulas from [Veithen2005] use the principal axe...
by jerkov
Mon Apr 06, 2020 12:44 am
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Andy, Thanks so much for your help! I finally got a beautiful DOS. One question though, I noticed that there's no option to include the direction of the non-analytic wavevectors generated by the wavevector grid(ng2qpt) near the zone center, which would be affected by the long-range force constant...
by jerkov
Mon Mar 30, 2020 6:58 pm
Forum: Response calculations
Topic: symmetry of phonon modes
Replies: 13
Views: 7296

Re: symmetry of phonon modes

Wow, I'm honored that X. Gonze would respond himself, and excited the new version of Abinit includes that update! Both your and Eric's responses clarify how to interpret the modes, and I successfully did for this example (reproducing the expected irreducible representation for 3m). In the source cod...
by jerkov
Wed Mar 25, 2020 3:13 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Okay, final question - so does that mean that nkpt in the main run has to have the same number of points as the qpts? In the RF2 tutorial, ngkpt = 4 4 4, and it looks like the qpts are determined by getting the symmetry inequivalent points from a 4x4x4 mesh. I can't tell if this is a coincidence, bu...
by jerkov
Tue Mar 24, 2020 11:13 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Andy, Okay, I read that paper. So Abinit uses a Fourier transform to take values of the dynamical matrix on a grid around the BZ (2x2x2 for example) in order to calculate the force constants and other derivatives needed to calculated phonon frequencies. After this main Abinit run when you build u...
by jerkov
Mon Mar 23, 2020 10:52 pm
Forum: Response calculations
Topic: symmetry of phonon modes
Replies: 13
Views: 7296

Re: symmetry of phonon modes

Hi Eric, So I finally got around to trying to match the irred. reps. based on the advice you gave. For example, for my R3m crystal (so C_3v point group), I get this symrel output when I run the main Abinit to get the phonons: symrel 1 0 0 0 1 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 0 0 0 1 0 1 0 0 0 0 1 0...
by jerkov
Mon Mar 23, 2020 10:08 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Andy, Thanks for the response. I tried lowering the number of qpts, but I don't think this run is using a supercell technique, right? Abinit uses DFPT to get around the supercell, frozen-phonon method for phonons. So while I agree, 12x12x12 is too much for this calculation, isn't 2x2x2 very few p...
by jerkov
Tue Mar 03, 2020 4:35 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Re: Phonon DOS [SOLVED]

Hi Andy, I run a GS calculation, and I set : ngkpt 12 12 12 kptopt 1 nshiftk 1 shiftk 0 0 0 prtkpt 1 nstep 1 nline 1 prtvol 2 #more than first 50 of kpts which makes the outfile contain all the kpoints used. This way, I generate all the symmetry inequivalent qpts needed to do a realistic integration...
by jerkov
Thu Feb 27, 2020 3:49 pm
Forum: Response calculations
Topic: Phonon DOS [SOLVED]
Replies: 19
Views: 1035

Phonon DOS [SOLVED]

Hi all, I have a question about calculating the phonon DOS, including the perturbation from the E field. I'm following RF2 (https://docs.abinit.org/tutorial/rf2/). As they suggest, to generate my phonon wavevectors, qpt, I first run a GS calculation. I'm using a low-symmetry monoclinic cell, so I en...
by jerkov
Thu Feb 27, 2020 3:38 pm
Forum: Response calculations
Topic: Zero Unit Cell Volume in Dispersion Calculation
Replies: 3
Views: 721

Re: Zero Unit Cell Volume in Dispersion Calculation

Hi Eric,

I'm confused by what you mean, as I think I do have three numbers: "scalecart 1 1 .9640"

I've used this exact unit cell in other calculations, and it hasn't given me zero volume.

Thanks!
by jerkov
Thu Feb 27, 2020 3:34 pm
Forum: Response calculations
Topic: symmetry of phonon modes
Replies: 13
Views: 7296

Re: symmetry of phonon modes

Thanks, Eric - that helps a lot!
by jerkov
Fri Jan 10, 2020 2:44 am
Forum: Response calculations
Topic: symmetry of phonon modes
Replies: 13
Views: 7296

Re: symmetry of phonon modes

How are you using symrel to get the irrep of your modes? I have this output after running anaddb: Analysis of degeneracies and characters (maximum tolerance=1.00E-06 a.u.) Symmetry characters of vibration mode # 1 degenerate with vibration modes # 2 to 3 3.0 1.0 Symmetry characters of vibration mode...
by jerkov
Mon Dec 30, 2019 4:30 pm
Forum: Response calculations
Topic: Zero Unit Cell Volume in Dispersion Calculation
Replies: 3
Views: 721

Zero Unit Cell Volume in Dispersion Calculation

Hi All, I'm following the RF2 tutorial (https://docs.abinit.org/tutorial/rf2/) to calculate the dispersion in a tetragonal unit cell. I've used the following unit cell parameters in other calculations without issue: acell 5 6 7 scalecart 1 1 .9640 rprim 1 0 0 0 1 0 0 0 1 But in this run, I'm now get...
by jerkov
Thu Dec 19, 2019 8:57 pm
Forum: Ground state
Topic: Relaxation, letting space group change [SOLVED]
Replies: 2
Views: 366

Re: Relaxation, letting space group change [SOLVED]

Thank you very much for the tip, ebousquet!