[Pw_forum] about "free" structure

[sun jason]

Dear all,

The dynmat.x will not work if I run the scf and phonon calculation with a 
"free" structure by ibrav=0 and specified lattice parameters. for instance, 
if I use 
-------------------------
 &SYSTEM
                       ibrav = 2,
                           A = 3.612 ,
                           B = 3.612 ,
                           C = 3.612 ,
                       cosAB = 0.0 ,
                       cosAC = 0.0 ,
                       cosBC = 0.0 ,
                         nat = 2,
                        ntyp = 2,
                     ecutwfc = 70.0 ,
 /
 &ELECTRONS
                    conv_thr = 1.0d-10 ,
                 mixing_beta = 0.7 ,
 /
ATOMIC_SPECIES
    B   10.81100  B.pbe.tm.UPF
    N   14.00674  N.pbe.tm.UPF
 
ATOMIC_POSITIONS (crystal)
B        0.000000000   0.000000000   0.000000000
N        0.250000000   0.250000000   0.250000000
K_POINTS automatic
  6 6 6   0 0 0
------------------------------------------

but the dynmat.x will not work if I use this structure.
------------------------------------------
 &SYSTEM
                       ibrav = 0,
                    celldm(1)= 6.831,
                         nat = 2,
                        ntyp = 2,
                     ecutwfc = 70.0 ,
 /
 &ELECTRONS
                    conv_thr = 1.0d-10 ,
                 mixing_beta = 0.7 ,
 /
ATOMIC_SPECIES
    B   10.81100  B.pbe.tm.UPF
    N   14.00674  N.pbe.tm.UPF
 
ATOMIC_POSITIONS (crystal)
B        0.000000000   0.000000000   0.000000000
N        0.250000000   0.250000000   0.250000000
K_POINTS automatic
  6 6 6   1 1 1
CELL_PARAMETERS
0.50 0.00 0.50
0.00 0.50 0.50
0.50 0.50 0.00
-------------------------------------------
 
the dynamical matrix file bn.dynG are almost same except the first line
>   2    2  2  6.8256935  1.0000000  1.0000000  0.0000000  0.0000000  
0.0000000
---
<   2    2  0  6.8310000  0.0000000  0.0000000  0.0000000  0.0000000  
0.0000000


so should I manually change this line if I want to use the second method 
using "ibrav=0 and cell parameters" to describe the crystal structures for 
some low symmetry ones, such as Triclinic; and cell parameters are more 
convenient to get from relaxtion result.

Thank you in advance


Best,
===============================================
Jian SUN 
Physics Dept. of Nanjing University 
National Lab. of Solid State Microstructures 
22 Hankou Road, Gulou District 
Nanjing, Jiangsu Province 
210093 
China 
===============================================