# non-orthorhomic variable cell optimization

Wed Feb 11 21:47:30 UTC 2009

```Hello everybody,

We seem to be having an issue with non-orthorhombic cell optimization
when the lattice has all the three angles other than 90 degrees. Here
is what appears to be happening: After the initial set up, the module
Changes the lattice vectors by keeping the lengths the same but the
angles are slightly different. This happens only when all the angles
are not 90-degrees. The regtest for non-orthorhombic includes only one
angle 120 and the rest are 90s. So the scenario I described might be
missed out. This issue we have observed in several executables we have
built over the last several months and on multiple architectures.

==================================================================================
Here is the output just after the set up which is the same as the
input:
CELL| Volume
[ANGSTROM**3]:                                             442.524
CELL| Vector a [ANGSTROM]:       9.010     0.000     0.000    |a|
=       9.010
CELL| Vector b [ANGSTROM]:      -4.510     7.821     0.000    |b|
=       9.028
CELL| Vector c [ANGSTROM]:      -0.216    -2.630     6.280    |c|
=       6.812
CELL| Angle (b,c)
[degree]:                                             108.580
CELL| Angle (a,c)
[degree]:                                              91.820
CELL| Angle (a,b)
[degree]:                                             119.970

Here is when it got changed just before the first step of the
optimization:

CELL| Volume
[ANGSTROM**3]:                                             449.960
CELL| Vector a [ANGSTROM]:       9.010     0.000     0.000    |a|
=       9.010
CELL| Vector b [ANGSTROM]:      -4.510     7.821     0.000    |b|
=       9.028
CELL| Vector c [ANGSTROM]:      -0.216    -2.363     6.386    |c|
=       6.812
CELL| Angle (b,c)
[degree]:                                             106.534
CELL| Angle (a,c)
[degree]:                                              91.820
CELL| Angle (a,b)
[degree]:                                             119.970
CELL| Grid size for subcell
generation                                    2.000

--------  Informations at step =     0 ------------
Optimization Method        =                   SD
Total Energy               =      -386.4717739715
Internal Pressure [bar]    =     18296.7247113471
---------------------------------------------------

--------------------------
OPTIMIZATION STEP:      1
=================================================================================
Could someone please take a look at this issue and let me know what
might be the issue.

Thanks

```