# region prism and number of atoms

Dear LAMMPS users,

I am working on a system having triclinic symmetry and having 3 types of total 72 atoms (4+20+48).
To create the lattice I used “custom” option along with region “prism” of LAMMPS.
I am trying to set up simulations of a crystal with triclinic box and lattice parameters as
a=a01.22474, b=a02.12132, c=a0*2.34521, α =98.67072, β =94.9933 and γ=90.

``````
> 1/2   1/2    -1  |
unit cell = a0 |-3/2   3/2     0  |
> 3/2     1     3/2|
I have calculated tilt factors based on relations
xy= bcosγ = 0.0,
xz=c*cosβ= -0.204125
yz = b*c cosα- xy*xz/Ly = -0.35355
lx=a=1.224745
ly^2=b^2-xy^2=2.12132
lz^2=c^2-xz^2-yz^2=2.309402
For the time being consider a0=1.0
Part of my input file looks like..

``````

How do you expect people to help you if you provide partial information? The lattice section of your script only shows 4 basis and then you just decided to cut it leaving anyone interested in looking at it totally at the mercy of their imagination. Get your act together first before asking people to invest their time into your project.

Carlos

PS: And putting together a readable input script always increases your chances of receiving prompt help. Avoid being labeled a “waste of time” case.

Dear LAMMPS users,
First of all I want to thank Carlos for pointing out my mistake in posting my problem.
Below I am giving my input script for perusal …

Dear LAMMPS users,
First of all I want to thank Carlos for pointing out my mistake in posting
my problem.
Below I am giving my input script for perusal ..

well, this is far to complex to debug it through reading. i wonder if
there would not be an easier way to do the same.

in any case, there is no obvious mistake, but there is one thing to
note. you provide the basis vectors with limited accuracy and at the
same time to provide lattice positions that would sit perfectly on a
box boundary. this combination can lead to the final atom positions
being located *outside* the box, if only by a tiny margin and LAMMPS
will not create those positions with create_atoms. since crystal
structures are invariant to translations, it is recommended to
translate the lattice or the system cell a little bit, so that these
inaccuracies resulting from the truncation have no effect.

since you specify each atom position individually, it should be easy
for you to verify this by commenting out all positions and re-enabling
them one by one and check, if the positions are properly created or
not.

axel.

I also wonder what kind of system is this. Do you really need such a convoluted way to define your unit cell? Moreover, are these supra-atoms of some sort? I don’t recognize the mass assignment you have in your input.

Looks to me the lattice issue might be one of many problems with your input. But maybe my superficial glace at ti is to blame. In any case, listen to Axel’s advice. he’s usually pretty much on target.

Carlos