[Pw_forum] on variable cell optimization
Serge Nakhmanson
nakhmans at physics.rutgers.edu
Fri Jan 28 16:58:54 CET 2005
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I have the same problem running version 2.1.2. I initially performed
a bfgs relaxation of the system with fixed volume and then started
volume relaxation reading in the "relaxed at fixed volume" configuration
as my starting point (was that a good idea?). This is what I have
at step 1 of vc-relax:
****************************************************************************
Total force = 0.000555 Total SCF correction = 0.000032
entering subroutine stress ...
total stress (ryd/bohr**3) (kbar) P= 8.79
-0.00000340 -0.00000002 -0.00000008 -0.50 0.00 -0.01
-0.00000002 0.00020133 0.00000013 0.00 29.62 0.02
-0.00000008 0.00000013 -0.00001863 -0.01 0.02 -2.74
Parrinello-Rahman Damped Cell-Dynamics Minimization
convergence thresholds: EPSE = 0.10E-03 EPSF = 0.10E-03 EPSP = 0.50E+00
Entering Dynamics; it = 1 time = 0.00000 pico-seconds
new lattice vectors (alat unit) :
0.999999998 0.000000000 0.000000000
0.000000000 1.194324076 0.000000000
0.000000000 0.000000000 1.144971993
new unit-cell volume = 5824.5998 (a.u.)^3
*****************************************************************************
And this is my situation after 28 steps:
*****************************************************************************
Total force = 0.000580 Total SCF correction = 0.000215
entering subroutine stress ...
total stress (ryd/bohr**3) (kbar) P= 8.64
-0.00000407 -0.00000002 -0.00000009 -0.60 0.00 -0.01
-0.00000002 0.00019975 0.00000012 0.00 29.38 0.02
-0.00000009 0.00000012 -0.00001940 -0.01 0.02 -2.85
Entering Dynamics; it = 28 time = 0.00131 pico-seconds
new lattice vectors (alat unit) :
0.999999081 -0.000000004 -0.000000022
-0.000000005 1.194369135 0.000000029
-0.000000025 0.000000028 1.144967629
new unit-cell volume = 5824.7920 (a.u.)^3
*****************************************************************************
This is the grep on pressure:
total stress (ryd/bohr**3) (kbar) P= 8.79
total stress (ryd/bohr**3) (kbar) P= 8.78
total stress (ryd/bohr**3) (kbar) P= 8.80
total stress (ryd/bohr**3) (kbar) P= 8.78
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.81
total stress (ryd/bohr**3) (kbar) P= 8.79
total stress (ryd/bohr**3) (kbar) P= 8.81
total stress (ryd/bohr**3) (kbar) P= 8.80
total stress (ryd/bohr**3) (kbar) P= 8.73
total stress (ryd/bohr**3) (kbar) P= 8.79
total stress (ryd/bohr**3) (kbar) P= 8.76
total stress (ryd/bohr**3) (kbar) P= 8.79
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.72
total stress (ryd/bohr**3) (kbar) P= 8.78
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.79
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.78
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.76
total stress (ryd/bohr**3) (kbar) P= 8.66
total stress (ryd/bohr**3) (kbar) P= 8.77
total stress (ryd/bohr**3) (kbar) P= 8.75
total stress (ryd/bohr**3) (kbar) P= 8.64
Nothing is moving, nothing is changing. I expected at least some cell relaxation along
the y-axis. Do I actually need to kick the system to see some relaxation? Or is
my cell too heavy (see below)? I've seen people asking questions about a good value
for cell mass but no answers have been given. Is that something that can be looked up
in Allen-Tildesley? BTW, what is the UMA unit ( cell mass = 36.00000 UMA )?
My input file is given below.
THX,
Serge
&control
calculation = 'vc-relax'
restart_mode='restart',
prefix='PVDF96.relax',
pseudo_dir = './',
outdir = './',
nstep = 100,
tstress = .true.,
max_seconds = 56000
etot_conv_thr = 1.0d-4
forc_conv_thr = 1.0d-4
/
&system
ibrav= 8,
nat= 96,
ntyp= 3,
celldm(1) = 16.210000,
celldm(2) = 1.194324,
celldm(3) = 1.144972,
ecutwfc = 30.0,
ecutrho = 270.0
nosym=.true.
/
&electrons
startingpot = 'file' ,
startingwfc = 'file' ,
mixing_mode = 'plain'
mixing_beta = 0.3
conv_thr = 1.0d-8
diagonalization = 'david' ,
&ions
upscale=10
ion_dynamics='damp'
potential_extrapolation='wfc2'
/
&cell
cell_dynamics='damp-pr'
wmass = 36.00
/
ATOMIC_SPECIES
F 12.01 F_pbe_us.van.UPF
C 12.01 C.pbe-van_bm.UPF
H 12.01 H.pbe-van_bm.UPF
ATOMIC_POSITIONS {bohr}
[ ... cut ... ]
K_POINTS {gamma}
Paolo Giannozzi wrote:
> On Thursday 27 January 2005 23:25, Eduardo Ariel Menendez P wrote:
>
>>I am trying to perorm a variable cell optimization
>
>
> version of the code?
>
- --
******************************************************************************
Serge M. Nakhmanson phone: +1 (732) 445-4603
Postdoctoral RA fax: +1 (732) 445-4400
Department of Physics & Astronomy
Rutgers, The State University of New Jersey
136 Frelinghuysen Road nakhmans at physics.rutgers.edu
Piscataway, NJ 08854-8019 http://www.physics.rutgers.edu/~nakhmans/
My GnuPG public key is here:
http://www.physics.rutgers.edu/~nakhmans/PGP/nakhmans_pubkey_current.asc
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