Willem,
Add the command
use_all_frac=.true.
to IIRC, this adjusts the FFT grid to be commensurate.
Alternatively, you can set the values of the FFT grid (nr1, nr2, nr3) by
hand. Depending on the fractional translation, making these integers
multiples of 2, 3, 4, or 6 should solve your
As pointed out by Giuseppe Mattioli, the ground state (A12) of Mn has a bcc
lattice, but not a 1 atom per unit cell structure. You can find the input
for the (29 atom) A12 structure, here:
http://aflow.org/CrystalDatabase/A_cI58_217_ac2g.html
and for the high temperature, 20 atom beta-Mn phase
It's impossible for space group #194 to have 15 atoms of one species and 1
atom of another species -- there aren't any Wyckoff positions in P6_3/mmc
that contain only one point.
What you've done eliminates the inversion operation, which changes #194 to
#187.
Take a look at both space groups in
We've updated the Library of Crystallographic Prototypes (the old NRL
Crystal Structure) site: http://www.aflowlib.org/CrystalDatabase/
First off, we added a sortable prototypes index (
http://www.aflowlib.org/CrystalDatabase/prototype_index.html), so you and
find any structure by its name,
, especially the alkali metals, DFT
is difficult.
On Wed, Aug 16, 2017 at 2:52 PM, Sunetra Das <sunetra.das...@gmail.com>
wrote:
>
> Dear Dr. Michael Mehl,
>
> Quoting you from your reply, "You must have minimum energy structure for
> your crystal structure at that volu
Density Functional Theory is not guaranteed to give a bulk modulus that
matches with experiment, unfortunately, though in most case I've tested it
has been within 10%.
In addition to the equation of state approach, you can try computing the
bulk modulus by numerical differentiation, using B(V) =
You've listed the Wyckoff positions of the atoms, which generate all of the
atoms in the unit cell. The space group for MoO3 is #62. Those points are
(4c) Wyckoff positions, which means that there are 16 atoms in the unit
cell.
There are two ways to handle this:
1) Investigate the crystal_sg
Finding the bulk modulus wth ev.x is essentially calculating
B(V) = V E''(V).
What the heck is E(V)? That's actually rather simple: E(V) is the minimum
energy of the the system at fixed volume. For your system,
E(V) = min eng(V,c/a) for all values of c/a at fixed volume V,
where
Should note that in the cP16 structure there will be relaxation around the
impurity atom. This doesn't happen in the smaller (cI16) cell because the
crystal symmetry won't allow it.
On Thu, May 25, 2017 at 9:44 AM, Michael Mehl <mm...@usna.edu> wrote:
> How is this for Fe_{1.7
How is this for Fe_{1.75}X_{0.25}:
http://aflow.org/CrystalDatabase/AB4C3_cI16_229_a_c_b.html
>From the prototype, change Ni -> Fe and Cr to whatever species you want.
This still has ibrav=3.
For the smaller impurity concentration, look at:
Hopefully many of you remember the old NRL Crystal Lattice Structures page,
which went dark a few years ago because I couldn't keep up with NRL's web
policies.
Now that I've moved the the US Naval Academy, and with help and support
from the AFLOW project (http://materials.duke.edu/), Duke
Since C and N are neighbors in the periodic table, you could put a
"virtual" atom at the site, with charge Z = 6.5. That would at least give
you the right electron count for the system and preserve the system
symmetry. The downside is that a pseudopotential for "Cargen" or
"Nitrobon" probably
Since pwscf doesn't recognize the (2/3,1/3,1/3) and (1/3,2/3,2/3)
fractional translations needed to populate the hexagonal cell, it's not
going to recognize that the Cu atoms are on the (3a) Wyckoff site, or Cr
on (3b). Given that, the small forces shown here are close enough to
zero so as to
You might try findsym: http://stokes.byu.edu/iso/findsym.php , where you
enter the primitive vectors and lattice coordinates, and the program
gives you the space group, conventional cell, and Wyckoff positions. For
Linux there is also downloadable command line version:
My apologies. Apparently it's restricted to NRL-only access for beta
testing. We should have things up and running fairly soon. Again,
sorry I jumped the gun.
On 12/6/12 9:44 AM, Michael Mehl wrote:
> I'm happy to report that the NRL Crystallographic Database is back on
> line.
I'm happy to report that the NRL Crystallographic Database is back on
line. It has, however, moved. The new address is
https://www.nrl.navy.mil/mstd/ccms/lattice/
I believe everything is functional except possibly the java plugin. If
you have any problems with the site, or see any errors,
I know many of the members of this list use the "Crystal Lattice
Structure" page at
http://cst-www.nrl.navy.mil/lattice/
to look up Crystal Structures for a variety of elements and compounds.
Due to a reconstruction of computer services at NRL, this page is going
to be unavailable for an
A shameless plug. The URL is to a preprint, but I'd appreciate the full
reference being used in your papers :-)
@InCollection{mehl94:fpcij,
author = {M. J. Mehl and B. M. Klein and D. A.
Papaconstantopoulos},
title ={First-Principles Calculation of Elastic Properties},
The elastic constants of sapphire are all in the 100-500 GPa range (same
reference as before). A 1 kbar error in your calculation, or even a 10
kbar (the pessimist in me says 100 kbar) is going to be small compared
to DFT errors. In general, trying to get elastic constants accurate to
1 kbar
And for other lattice systems have a look at the Bilbao Crystallographic
Server's k-point and Brillouin zone page:
http://www.cryst.ehu.es/cryst/get_kvec.html
which covers all the lattice types and space groups.
(What can I say? They have graduate students, I don't.)
On 03/29/2012 06:26 AM,
It's base-centered orthorhombic, so that would be #9
http://cst-www.nrl.navy.mil/lattice/struk/a11.html
Generally "A", "B", or "C" in the space group's International Symbol
denotes a base-centered system, be it monoclinic or orthorhombic.
On 02/14/2012 04:04 PM, Payam Norouzzadeh wrote:
>
which has a CsCl structure with ibrav
> = 3 and atomic position 0 0 0 for Ni atom and 0.5 0.5 0.5 for Al atom.
> I am using xcrysden to view the structure, I only see Ni atoms and with
> no Al atom in the matrix. Can anybody please tell me where I am going
> wrong. I have my input file
Bipul Rakshit wrote:
> Dear Michael Mehl,
> I have read the two papers
> http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf
>
> and
>
> Phys. Rev. B 47, 2493 (1993)
> ,
> But my question is, they have given only two equation, and our unknown
> quantity are
Bipul Rakshit wrote:
> Because in order to calculate 3 elastic constants (C11, C12 and C44) we
> require 3 equations, so do I have to use the above three equations, both
> type (volume conservative and non-conservative) to calculate a single
> set of elastic constants?
Yes.
>
> please guide
"units" [ http://en.wikipedia.org/wiki/Units_(Unix) ] is your friend
$ units
2445 units, 71 prefixes, 33 nonlinear units
You have: 1 rydberg/bohrradius^3
You want: gigapascal
* 14710.505
/ 6.7978632e-05
With the Ubuntu version, at least, using "au" instead of "bohrradius"
Miguel Marti?nez wrote:
> Given the column formatting of the output, I usually go for gnuplot,
> although long lines are a pain* on an interactive gnuplot session. Regards,
>
> Miguel
>
> * Even more so when Debian/Ubuntu packages are built without filename
> completion.
>
>
I can actually
Dev,
I believe that if you look closely at the published band structures of
graphene you'll find that many graphs are centered on the K
point. This doesn't mean that the K point is now the origin, it just
means that the K point is the center of the published graph. That's
because K is the
information so that I can actually
reconstruct the unit cell. And thank you, Miguel.
Miguel Mart?nez Canales wrote:
> Dear Michael,
>
> Michael Mehl escribi?:
>> Well, this would work, if _I_ knew the structure of In2S3. If someone
>> figures it out, send the structural informati
Well, this would work, if _I_ knew the structure of In2S3. If someone
figures it out, send the structural information to my work address
(mehl at dave.nrl.navy.mil) and I'll put it on the web page.
Serge Nakhmanson wrote:
> It is always better to teach a person how to fish, though!
>
> Look
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