[Pw_forum] about the variable-cell MD

[Artem R. Khabibullin]

Dear colleagues,
I am beginner user of the Quantum-Espresso. My task is the simulation 32
water molecules (H2O). I have still some problems. The main of them is a
variable-cell MD with cp.x code under constantly high pressure in the (NpT -
ensemble). Another words, I am exploring 32 molecules of water under high
pressure and specific temperature. My script to this case is

# Electronical + Ionic Dynamics + NOSE thermostat on ions +

&CONTROL
title = ' Water 32 Molecules ',
calculation = 'vc-cp',
restart_mode = 'restart',
ndr = 51,
ndw = 52,
nstep = 2000,
iprint = 10,
isave = 10,
tstress = .TRUE.,
tprnfor = .TRUE.,
dt = 4.0d0,
etot_conv_thr = 1.d-9,
ekin_conv_thr = 1.d-4,
prefix = 'h2o_mol'
pseudo_dir = './pseudo/'
outdir = './tmp/'
/

&SYSTEM
ibrav = 14,
celldm(1) = 18.65,
celldm(2) = 1.0,
celldm(3) = 1.0,
celldm(4) = 0.0,
celldm(5) = 0.0,
celldm(6) = 0.0,
nat = 96,
ntyp = 2,
nbnd = 128,
nelec = 256,
ecutwfc = 70.0,
ecfixed = 68.0,
qcutz = 68.0,
q2sigma = 8.0,
xc_type = 'BLYP',
/

&ELECTRONS
emass = 300.d0,
emass_cutoff = 2.5d0,
orthogonalization = 'ortho',
electron_dynamics = 'verlet',
electron_velocities = 'zero',
ortho_eps = 5.d-8,
ortho_max = 15,
/

&IONS
ion_dynamics = 'verlet',
ion_temperature = 'nose',
!ion_velocities = 'zero',
tempw = 277.0,
fnosep = 48,

ion_radius(1) = 0.8d0,
ion_radius(2) = 0.5d0,
/

&CELL
cell_dynamics = 'pr',
!cell_velocities = 'zero',
press = 0.2d0,
wmass = 79859.24
/

ATOMIC_SPECIES
O 16.0d0 O.BLYP.UPF 4
H 1.0079d0 H.fpmd.UPF 4

ATOMIC_POSITIONS (crystal) !(bohr)
O 0.3342 0.3858 0.1702
O 0.6681 0.0772 0.0996
O 0.4894 0.2752 0.9664
O 0.8374 0.0165 0.8885
O 0.4164 0.1406 0.5374
O 0.9200 0.2746 0.7479
O 0.9298 0.6759 0.0546
O 0.5197 0.5773 0.2470
O 0.8453 0.2308 0.2531
O 0.7080 0.4512 0.1102
O 0.6297 0.6739 0.4697
O 0.6889 0.4428 0.8100
O 0.9273 0.8859 0.2748
O 0.7260 0.9572 0.4514
O 0.9539 0.6297 0.6304
O 0.0634 0.4197 0.2665
O 0.0088 0.1409 0.5073
O 0.8042 0.4375 0.4942
O 0.6981 0.1893 0.5833
O 0.2908 0.5198 0.5234
O 0.1835 0.3971 0.7808
O 0.2450 0.2024 0.3474
O 0.3062 0.1574 0.7995
O 0.4465 0.8389 0.2161
O 0.1931 0.5738 0.0049
O 0.1879 0.9665 0.1899
O 0.0876 0.6667 0.4085
O 0.2637 0.7476 0.7879
O 0.5203 0.6329 0.7214
O 0.3714 0.8763 0.4899
O 0.7915 0.8290 0.7054
O 0.1436 0.9899 0.9297
H 0.3742 0.3360 0.0929
H 0.3150 0.3226 0.2472
H 0.9405 0.1804 0.4516
H 0.6062 0.0086 0.1372
H 0.7231 0.0354 0.0264
H 0.5460 0.2002 0.9884
H 0.5502 0.3269 0.9029
H 0.8537 0.1049 0.8480
H 0.4251 0.0432 0.5210
H 0.3722 0.1543 0.6275
H 0.7041 0.0486 0.4909
H 0.9378 0.2191 0.6620
H 0.9083 0.7339 0.1314
H 0.5940 0.5403 0.1919
H 0.4413 0.5140 0.2303
H 0.7975 0.1623 0.1939
H 0.9351 0.2490 0.2169
H 0.7495 0.3794 0.1764
H 0.7769 0.5261 0.0949
H 0.7242 0.6488 0.4514
H 0.5812 0.6156 0.4033
H 0.7610 0.3991 0.7586
H 0.7253 0.4549 0.9012
H 0.9805 0.8118 0.3158
H 0.8774 0.9234 0.3508
H 0.8266 0.9432 0.8185
H 0.6439 0.9054 0.4658
H 0.9099 0.7082 0.6739
H 0.1146 0.3475 0.3129
H 0.1177 0.4592 0.1936
H 0.0984 0.1864 0.4941
H 0.8732 0.4903 0.5432
H 0.8466 0.4047 0.4105
H 0.5983 0.1849 0.5758
H 0.7255 0.2866 0.5619
H 0.2468 0.6010 0.4948
H 0.3655 0.5512 0.5766
H 0.2218 0.4478 0.6984
H 0.2272 0.3027 0.7736
H 0.0089 0.3172 0.7749
H 0.3206 0.1756 0.4126
H 0.2308 0.1250 0.2800
H 0.2420 0.1027 0.8550
H 0.3752 0.1963 0.8703
H 0.3477 0.8559 0.1901
H 0.4738 0.7418 0.2103
H 0.0297 0.6626 0.0605
H 0.2668 0.5360 0.0599
H 0.1691 0.9883 0.0958
H 0.0952 0.9378 0.2237
H 0.0161 0.6488 0.4768
H 0.0940 0.5739 0.3729
H 0.2728 0.6995 0.8762
H 0.3551 0.7479 0.7517
H 0.5812 0.5576 0.7579
H 0.5605 0.6617 0.6349
H 0.1741 0.5139 0.9284
H 0.3026 0.8058 0.5084
H 0.4067 0.8573 0.3940
H 0.7040 0.7965 0.7365
H 0.7716 0.8608 0.6097
H 0.0148 0.6043 0.7064
H 0.1834 0.9112 0.8662
H 0.0492 0.9894 0.9207

KSOUT
2
1 4

this is 7 step, when the system is relaxing and there is the electron and
ion dynamics and then at the 7 step I have adding the pressure on system.
The value for "wmass" in CELL section I got from the previous step. During
the calculation I have one problem: in the step7.out file the value of
(XNHH0 - position of Nose' for cell) became equals to infinity from
approximately 1000-1500 time steps. Why is it?
I will be very glad for answer on this problem.

-----------------------------------------------------------------
With best wishes, Artem R.

Dr. Artem R. Khabibullin
Department of Theoretical Physics,
Kazan Federal University.
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