# [Pw_forum] from ibrav=0 to 1

li niu niuli1978 at yahoo.com.cn
Wed May 23 15:51:45 CEST 2007

```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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