[Pw_forum] from ibrav=0 to 1

[degironc]

If vc-relaxation produces a non-cubic solution then the system is likely
to be non-cubic.
In any event if you insist in using a cubic set-up it could be more
convenient to give the
atomic coordinates in crystal format so that they are automatically
scaled according to the
modified cell-edge dimensions
regards,
stefano

li niu wrote:
> Dear all,
> After many vc-relax calculations(first ibrav=1,then using ibrav=0, new
> cell_parameters, new positions), I obtained
> the following results. It is obvious the cell angle parameters have
> been changed and the structure isn't the cubic structure.
>
> 1. If I still set ibrav=1 in the next scf calculation, how to read the
> new lattice constant?
> I have attempted to use celldm(1)*(a11+a22+a33)/3 as the new celldm(1),
> (axx is the diagonal element of cell_parameters) ,the output
> atomic_positions(alat) as the new atomic_positions,and neglect all of
> the nondiagonal elements.
> After the first self-consistent,I gain stresses with very large value.
> How can I adapt the input parameters to avoid this condition and get
> smaller elements?
>
> 2.Must the k-points are same in the vc-relax and scf?
> any help will be appreciated!
>
> Best!
> Niu Li
> Harbin Institute of Technology
> China
> ==================================================
> ! total energy = -729.30084995 Ry
> Harris-Foulkes estimate = -729.30084995 Ry
> estimated scf accuracy < 8.1E-10 Ry
> convergence has been achieved
> Forces acting on atoms (Ry/au):
> atom 1 type 1 force = 0.00000028 -0.00000032 -0.00000017
> ...
> atom 62 type 1 force = -0.00000135 0.00000206 0.00000190
> atom 63 type 1 force = -0.00000012 -0.00000115 0.00000144
> atom 64 type 1 force = -0.00000077 -0.00000041 -0.00000140
> Total force = 0.000024 Total SCF correction = 0.000091
>
> entering subroutine stress ...
> total stress (Ry/bohr**3) (kbar) P= 0.06
> 0.00000025 0.00000101 0.00000074 0.04 0.15 0.11
> 0.00000101 0.00000338 -0.00000180 0.15 0.50 -0.27
> 0.00000074 -0.00000180 -0.00000237 0.11 -0.27 -0.35
>
> Wentzcovitch Damped Dynamics: convergence achieved, Efinal= -729.30084995
> ------------------------------------------------------------------------
> Final estimate of lattice vectors (input alat units)
> 0.988103212 0.021498496 -0.002655708
> 0.021493430 1.013103454 -0.000556700
> -0.002655491 -0.000556401 0.983829644
> final unit-cell volume = 2649.6086 (a.u.)^3
> input alat = 13.9103 (a.u.)
> CELL_PARAMETERS (alat)
> 0.988103212 0.021498496 -0.002655708
> 0.021493430 1.013103454 -0.000556700
> -0.002655491 -0.000556401 0.983829644
> ATOMIC_POSITIONS (angstrom)
> C 0.292559767 -0.288781798 -0.891844186
> C 1.355532741 -0.743068572 3.628414295
> ...
> C 3.388679954 3.539286798 4.255326154
> =========================================
>
> ------------------------------------------------------------------------
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