[DFTB-Plus-User] Monoclinic unit cell ... Cell parameters constrains ...

[Michal Husak]

Hi

I am not sure how to correctly perform optimization of a 
monoclinic  crystal unit cell ...

FixAngles = Yes is OK for orthorhombic and higher symmetry ...
FixAngles = No is OK for triclinic
FixAngles = No is OK for rhombic, BUT all angle should be equal ...

But monoclinic require to fix only alpha and gamma, beta should be free ...

Similar issue is with FixLengths ...

The lengths should be constrained according crystallographic system.

a=b=c for cubic and rhombic
a=b for hexagonal and  tetragonal

Is there any chance to be able for lattice parameters:
- fix values individually ?
- link values so they change identical ?

Or preferably be able to input crystal system and generated automatic 
correct setup ...

To be able to input space group symmetry is another story, but this 
is something we can handle on our side ...

Michal Husak
UCT Prague