ABINIT Discussion Forums

Hi,

I'd like to repeat this question, as it's something with which 'm still struggling!

Best,
J

Hi Eric, I don't mean to be pedantic, but looking closer at the symmetry relations and then the symmetry characters my run produced, I think the order the matrices are read is different from what you wrote. If symrel prints: 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 ...

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...

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...

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...

Hi Eric,

That makes sense, thanks a bunch!

J

Hi everyone,

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

J

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...

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...

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 ...

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 ...

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...

Great! All good then. You can mark this as 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...

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...

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...

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...

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...

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...

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...

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...

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...

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!

Thanks, Eric - that helps a lot!

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...