# Alpha Quartz unit cell structure

Dear all,

I have been going up and down the mailing list for the unit cell of alpha Quartz in lammps, but I have seen different codes. I haven’t tried it yet but I think this one, mentioned by Steve, is correct:

``````lattice custom 5.4047 origin 0.0 0.0 0.0 &
spacing 0.909153 0.78734976 1 &
a1 0.909153 0.000000 0.00000000 &
a2 -0.454576598 0.78734976 0.00000000 &
a3 0.00000000 0.00000000 1.00000000 &
basis  0.46990000  0.00000000  0.66666667 &
basis  0.00000000  0.46990000  0.33333333 &
basis  0.53010000  0.53010000  0.00000000 &
basis  0.41410000  0.26810000  0.78540000 &
basis  0.73190000  0.14600000  0.45206667 &
basis  0.85390000  0.58589999  0.11873333 &
basis  0.26810000  0.41410000  0.21460000 &
basis  0.58589999  0.85399999  0.88127777 &
basis  0.14600000  0.73190000  0.54793333
region simbox prism 0 1 0 1 0 1 -0.454576598 0 0

I have seen different codes in which a2 is like
a2 0.0 0.78734976 0.0
I don;t know how it is calculated.
Questions:
How a1,a2, and a3 values are calculated?
How basis values are calculated?
Is it possible to achieve these parameter only by using this:

Quartz
Levien L, Prewitt C T, Weidner D J
American Mineralogist 65 (1980) 920-930
Structure and elastic properties of quartz at pressure
P = 1 atm
_database_code_amcsd 0000789
4.916 4.916 5.4054 90 90 120 *P3_221
0 0 .666666667
atom     x     y     z B(1,1) B(2,2) B(3,3) B(1,2)  B(1,3)  B(2,3)
Si   .4697     0     0  .0093  .0078  .0049  .0039 -.00001 -.00002
O    .4135 .2669 .1191  .0190  .0144  .0083  .0106 -.00250  -.0035

I know this might sound like a dumb qquestion, but I am a civil engineer and very new to this field of study.

PS: My final goal is to calculate the tensile strength (and other mechanical properties) of alpha quartz.

Sincerely,

``````

Dear all,

I have been going up and down the mailing list for the unit cell of alpha
Quartz in lammps, but I have seen different codes. I haven't tried it yet
but I think this one, mentioned by Steve, is correct:

lattice custom 5.4047 origin 0.0 0.0 0.0 &
spacing 0.909153 0.78734976 1 &
a1 0.909153 0.000000 0.00000000 &
a2 -0.454576598 0.78734976 0.00000000 &
a3 0.00000000 0.00000000 1.00000000 &
basis 0.46990000 0.00000000 0.66666667 &
basis 0.00000000 0.46990000 0.33333333 &
basis 0.53010000 0.53010000 0.00000000 &
basis 0.41410000 0.26810000 0.78540000 &
basis 0.73190000 0.14600000 0.45206667 &
basis 0.85390000 0.58589999 0.11873333 &
basis 0.26810000 0.41410000 0.21460000 &
basis 0.58589999 0.85399999 0.88127777 &
basis 0.14600000 0.73190000 0.54793333
region simbox prism 0 1 0 1 0 1 -0.454576598 0 0

I have seen different codes in which a2 is like
a2 0.0 0.78734976 0.0
I don;t know how it is calculated.
Questions:
How a1,a2, and a3 values are calculated?
How basis values are calculated?
Is it possible to achieve these parameter only by using this:

Quartz
Levien L, Prewitt C T, Weidner D J
American Mineralogist 65 (1980) 920-930
Structure and elastic properties of quartz at pressure
P = 1 atm
_database_code_amcsd 0000789
4.916 4.916 5.4054 90 90 120 *P3_221
0 0 .666666667
atom x y z B(1,1) B(2,2) B(3,3) B(1,2) B(1,3) B(2,3)
Si .4697 0 0 .0093 .0078 .0049 .0039 -.00001 -.00002
O .4135 .2669 .1191 .0190 .0144 .0083 .0106 -.00250 -.0035

I know this might sound like a dumb qquestion, but I am a civil engineer and
very new to this field of study.

...and that is the main reason why you should follow the advice of
aidan thompson has been given you, rather than ignoring it.
you also do need to learn what a space group is and how you can
generate coordinates in a conventional cell from it.
but more importantly, you need to learn basic MD/MM methodology and
that is best done with simpler systems.

you are currently trying solve the third problem before the first. be
prepared that people will not consider that you are new to the field
as a valid justification for skipping ahead.

axel.