# non-orthorhomic variable cell optimization

Tue Feb 17 15:54:00 UTC 2009

```Dear Monica,

Thank you for your response and I really appreciate it. I would like
to clarify further about my earlier posting as it relates to the
behavior of the variable cell optimization module.

We are getting reasonable results using the variable cell optimization
module when it comes to non-monoclinic cells. But We have observed
consistently in the case of triclinic cells is a change in the lattice
vectors from the given input even before taking an optimization step.
It is as if the module is starting with a different initial
configuration.

Our intention is to understand the process the module follows so that
we can be comfortable with the final output it produces. For example,
in one of our studies we gave the following input:

In this case we are providing the experimental lattice configuration
as the input.

CELL| Vector a [ANGSTROM]:       9.814     0.000     0.000    |
a|      =       9.814
CELL| Vector b [ANGSTROM]:       0.424     9.038     0.000    |b|
=       9.048
CELL| Vector c [ANGSTROM]:       1.575     0.001    20.279    |c|
=      20.340
CELL| Angle (b,c)
[degree]:                                              89.790
CELL| Angle (a,c)
[degree]:                                              85.559
CELL| Angle (a,b)
[degree]:                                              87.314

Then after the initial set up the module prints the following
configuration at the 0th step: (This 0th step is before any prior
calculation has happened)
ANGSTROM**3]:                                            1795.645
CELL| Vector a [ANGSTROM]:       9.807     0.000     0.000    |a|
=       9.807
CELL| Vector b [ANGSTROM]:       0.424     9.031     0.000    |b|
=       9.041
CELL| Vector c [ANGSTROM]:       1.575    -0.001    20.276    |c|
=      20.337
CELL| Angle (b,c)
[degree]:                                              89.795
CELL| Angle (a,c)
[degree]:                                              85.559
CELL| Angle (a,b)
[degree]:                                              87.312

This strange switch in the initial geometry is happening only in the
case of triclinic cells. In addition, the final output volume is off
by more than 10% in some cases. This is what prompted us to go over
the output in detail and come up with a pattern.
It would help us understand and be comfortable with the results if we
know what is happening at the 0th step and what prompts the change in
the configuration only for monoclinic cells.

If the developers can take a look at the pattern and provide us with
any suggestions we would appreciate it.

Thanks

On Feb 13, 9:33 am, monica <monic... at phys.chem.ethz.ch> wrote:
>
> I was running recently several triclinic cell optimization jobs
> (although the angles are very close to 90), with variable hydrostatic
> pressure (0-20 GPa), and it seemed to work: when comparing the volume
> with similar orthorhombic cell, optimized manually (energy volume
> curve). See output below for example. In my case, when the cell was
> already close to the minimum, only minor changes occurred.
>
> Monica
>
> output for example
>  CELL| Volume
> [ANGSTROM**3]:                                            1798.737
>  CELL| Vector a [ANGSTROM]:       9.814     0.000     0.000    |a|
> =       9.814
>  CELL| Vector b [ANGSTROM]:       0.424     9.038     0.000    |b|
> =       9.048
>  CELL| Vector c [ANGSTROM]:       1.575     0.001    20.279    |c|
> =      20.340
>  CELL| Angle (b,c)
> [degree]:                                              89.790
>  CELL| Angle (a,c)
> [degree]:                                              85.559
>  CELL| Angle (a,b)
> [degree]:                                              87.314
>  CELL| Grid size for subcell
> generation                                    2.000
>  CELL| Volume
> [ANGSTROM**3]:                                            1795.645
>  CELL| Vector a [ANGSTROM]:       9.807     0.000     0.000    |a|
> =       9.807
>  CELL| Vector b [ANGSTROM]:       0.424     9.031     0.000    |b|
> =       9.041
>  CELL| Vector c [ANGSTROM]:       1.575    -0.001    20.276    |c|
> =      20.337
>  CELL| Angle (b,c)
> [degree]:                                              89.795
>  CELL| Angle (a,c)
> [degree]:                                              85.559
>  CELL| Angle (a,b)
> [degree]:                                              87.312
>  CELL| Grid size for subcell
> generation                                    2.000
>  CELL| Volume
> [ANGSTROM**3]:                                            1785.878
>  CELL| Vector a [ANGSTROM]:       9.783     0.000     0.000    |a|
> =       9.783
>  CELL| Vector b [ANGSTROM]:       0.424     9.008     0.000    |b|
> =       9.018
>  CELL| Vector c [ANGSTROM]:       1.574    -0.006    20.266    |c|
> =      20.327
>  CELL| Angle (b,c)
> [degree]:                                              89.810
>  CELL| Angle (a,c)
> [degree]:                                              85.560
>  CELL| Angle (a,b)
> [degree]:                                              87.307
>
>
>
>
> > 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
> > Rad- Hide quoted text -
>
> - Show quoted text -
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