[Pw_forum] cell_dofree

[Federico Gallino]

Dear All,

I write you about an issue I found in the use of the cell_dofree option.
I want to make a variable cell optimization by fixing the lattice angles and varying only
the lattice axis lengths. It should correspond to cell_dofree = 'xyz' but it doesn't work
for any cells I tested.
Below you can  find the input.

Moreover, a more general question concerns the constrained optimization: is it possible to
impose a constrain on two or more lattice parameters so that they can vary of the same
amount? This for example would allow to optimize a cubic cell that for convenience becomes
orthorombic by applying a supercell: after a constrained optimization where the lattice
parameters ratio are constrained, you will get still a cubic symmetry even though you
worked on an orthorombic cell. Is this possible in your opinion?

Thanking you in advance,


Federico Gallino


!test
         &CONTROL
	       title = 'sampleA' ,
	 calculation = 'vc-relax' ,
	  pseudo_dir = '/QUANTUM_ESPRESSO/espresso-5.0.2/pseudo/' ,
	      prefix = 'sampleA' ,
	   verbosity = 'default' ,
 /
 &SYSTEM
	       ibrav = 0,
           celldm(1) = 16.11503102 ,
		 nat = 32,
		ntyp = 3,
	     ecutwfc = 27 ,
	     ecutrho = 270 ,
	 occupations = 'smearing' ,
	    smearing = 'cold',
	     degauss = 0.03 ,
 /
 &ELECTRONS
    electron_maxstep = 200,
	 startingpot = 'atomic' ,
	 startingwfc = 'atomic' ,
	 mixing_mode = 'local-TF' ,
	 mixing_beta = 0.2 ,
     diagonalization = 'david' ,
 /
 &IONS
	ion_dynamics = 'bfgs' ,
	 phase_space = 'full' ,
 /
 &CELL
       cell_dynamics = 'bfgs' ,
	cell_dofree = 'xyz' ,
 /
CELL_PARAMETERS alat
   0.000000   0.707107   0.707107
   0.707107   0.000000   0.707107
   0.707107   0.707107   0.000000
ATOMIC_SPECIES
......
ATOMIC_POSITIONS   angstrom
.....
K_POINTS automatic
3 3 3   0 0 0

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