[QE-users] change lattice constant for orthorhombic structure

[Pooja Vyas]

Dear Sir,
I did a vc-relax calculation once to obtain the equilibrium parameters at
zero pressure. Will surely try the way you suggested. But is it possible to
compute E(V), if yes, then how should I be varying the lattice parameters
A, B and C? Attached below is my input file.
Regards.

On Wed, Oct 27, 2021 at 3:37 PM Davide Ceresoli <davide.ceresoli at cnr.it>
wrote:

> Instead of doing a constant volume relaxation (calculation='relax'),
> do a constant pressure relaxation (calculation='vc-relax', press=....).
> This way you will obtain E(V) where E=E(P), V=V(P) and the enthalpy
> H(P) = E(P) + P*V(P).
>
> HTH.
>
> D.
>
>
>
> On 10/27/21 11:05 AM, Pooja Vyas wrote:
> > Dear users,
> > I have obtained equilibrium parameters for my orthorhombic system which
> has
> > ibrav=8 and lattice constants A, B and C in Angstroms. Now, I need
> energy vs.
> > lattice constant curve, for which I require to change the lattice
> constant. For
> > a cubic system only 'a' is used and hence only 'a' used to change. But
> can I
> > know what could be the correct way for changing lattice constants for
> > orthorhombic? If I change 'a' in step of 0.05 angstrom, then how should
> I change
> > B and C?
> >
> > Any kind of help is appreciated.
> _______________________________________________
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 &control
    calculation = 'vc-relax',
    prefix = 'scf_equil'
    tprnfor=.true.
    tstress=.true.
    outdir = '/home/userpooja/PNV/CaSiO3_orthorhombic/CaSiO3_ortho/'
    pseudo_dir = '/home/userpooja/PNV/CaSiO3_orthorhombic/CaSiO3_ortho/pseudo2/'
 /
 &system
    ibrav =  8, 
    A=4.997425691
    B=5.018683212
    C=7.050142273	 
    nat =  20, 
    ntyp = 3,
    ecutwfc = 80,
/    
&electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-12
/
&IONS
/
&CELL
press = 0
/
ATOMIC_SPECIES
 
Ca 40.078  Ca.pz-spn-kjpaw_psl.1.0.0.UPF
Si 28.0855 Si.pz-n-kjpaw_psl.0.1.UPF
 O 15.999   O.pz-n-kjpaw_psl.0.1.UPF

ATOMIC_POSITIONS (crystal)
Ca            0.0063868436        0.4985789577        0.7500000000
Ca            0.4936131564        0.9985789577        0.2500000000
Ca            0.5063868436        0.0014210423        0.7500000000
Ca            0.9936131564        0.5014210423        0.2500000000
Si           -0.0000000000       -0.0000000000        0.5000000000
Si            0.0000000000       -0.0000000000        0.0000000000
Si            0.5000000000        0.5000000000        0.0000000000
Si            0.5000000000        0.5000000000        0.5000000000
O             0.0007786313        0.0394514856        0.2500000000
O             0.2393683165        0.7394625233        0.4797388476
O             0.2393683165        0.7394625233        0.0202611524
O             0.2606316835        0.2394625233        0.9797388476
O             0.2606316835        0.2394625233        0.5202611524
O             0.4992213687        0.5394514856        0.7500000000
O             0.5007786313        0.4605485144        0.2500000000
O             0.7393683165        0.7605374767        0.4797388476
O             0.7393683165        0.7605374767        0.0202611524
O             0.7606316835        0.2605374767        0.5202611524
O             0.7606316835        0.2605374767        0.9797388476
O             0.9992213687        0.9605485144        0.7500000000


K_POINTS (automatic)
  10 10 10 1 1 1