[lammps-users] Question about 'fix npt drag'

Hi all,

My lammps version is LAMMPS 7 Aug 2019.

I’m trying to restart a simulation using ‘fix npt drag’ with specific stress fields, as the same as the previous simulation. However, after I restart it, I observe that the system is further relaxed. So my question is why it can be further relaxed, if the system has been equilibrated already.(part of log.lammps is attached below).

My second question is about ‘drag’. The documentation says a value of drag from 0 to 2 is recommended, but what if I use a value out of this range? Is it always more accurate for the calculation by using drag 0.0?

Thanks in advance.

-----------------------log.lammps-----------------------

LAMMPS (7 Aug 2019)

package gpu 1

package gpu 4 neigh no

units real

dimension 3

processors * * *

boundary p p p

atom_style full

bond_style harmonic

angle_style harmonic

dihedral_style harmonic

improper_style harmonic

box tilt large

read_restart 0.58_npt.50000

restoring atom style full from restart

triclinic box = (-8.03092 0.00382625 -7.29379) to (750.291 5.59814 431.573) with tilt (3.35439 -422.822 1.13621)

WARNING: Triclinic box skew is large (…/domain.cpp:191)

20 by 1 by 18 MPI processor grid

restoring pair style buck/coul/long/gpu from restart

restoring bond style harmonic from restart

restoring angle style harmonic from restart

restoring dihedral style harmonic from restart

restoring improper style harmonic from restart

196000 atoms

196000 bonds

336000 angles

616000 dihedrals

56000 impropers

4 = max # of 1-2 neighbors

8 = max # of 1-3 neighbors

18 = max # of special neighbors

special bonds CPU = 0.0393438 secs

read_restart CPU = 0.128474 secs

suffix off

kspace_style pppm 1.0e-6

neighbor 2.0 bin

neigh_modify delay 0 every 1 check yes one 10000 page 100000

compute 1 all temp

compute PE all pe/atom

compute KE all ke/atom

compute eng all pe/atom

compute eatoms all reduce sum c_eng

compute stress all stress/atom NULL

variable deform_temp equal 300

variable natoms equal “count(all)”

variable totaleng equal “c_eatoms”

variable p1 equal “-pxx*0.000101325”

variable p2 equal “-pyy*0.000101325”

variable p3 equal “-pzz*0.000101325”

variable p4 equal “-pxy*0.000101325”

variable p5 equal “-pxz*0.000101325”

variable p6 equal “-pyz*0.000101325”

variable beta equal “(180/PI)*atan2(lz,xz)”

variable beta0 equal ${beta}

variable beta0 equal 133.933251002877

variable volume equal “vol”

reset_timestep 0

fix 6 all npt temp 300 300 1000 x 0 0 10000 y 0 0 10000 z 0 0 10000 xy 0 0 10000 xz 5724.15494695 5724.15494695 5000 yz 0 0 10000 drag 2.5

Per MPI rank memory allocation (min/avg/max) = 49.75 | 50.18 | 50.75 Mbytes

Step PotEng KinEng Lx Ly Lz Press v_p1 v_p2 v_p3 v_p4 v_p5 v_p6 Volume v_beta Temp

0 2954623.8 175081.12 758.322 5.594311 438.86662 -584.21184 0.14068679 0.026887304 0.010011704 -0.016463057 -0.5657237 -0.010756127 1861799.1 133.93325 299.67544

100 2954599.9 175090.29 758.30961 5.5943111 438.86645 -326.65405 0.11336355 -0.023410304 0.0093414152 0.036155874 -0.54682787 -0.0037388647 1861768 133.93275 299.69113

200 2954710.9 174993.03 758.275 5.594318 438.86643 -584.4238 0.18883198 -0.019026572 0.0078448177 0.0012748915 -0.60610628 0.0075393467 1861685.2 133.93131 299.52467

300 2954725 174979.72 758.22082 5.5943214 438.86666 -349.96376 0.14657386 -0.024845016 -0.015348608 -0.023957515 -0.61698766 -0.019158563 1861554.3 133.92896 299.50189

400 2954580.8 175112.19 758.14892 5.5943282 438.867 -619.83946 0.13500707 0.032196373 0.021212252 0.035450728 -0.57276343 -0.0034715761 1861381.5 133.92579 299.72862

500 2954648.9 175026.52 758.06098 5.5943403 438.86766 -362.35853 0.1612342 -0.030706813 -0.020379454 -0.0050683777 -0.5818497 0.027980516 1861172.4 133.92192 299.58199

600 2954418.9 175256.64 757.95969 5.5943576 438.86853 -606.23625 0.17269513 0.0038845399 0.0077009892 -0.036015296 -0.62653821 0.0088916706 1860933.1 133.91752 299.97588

700 2954356.1 175304.68 757.84762 5.5943764 438.86976 -484.75679 0.14919756 -0.0042811667 0.0024375551 0.053935657 -0.58532011 -0.0043438141 1860669.5 133.91253 300.05809

800 2953851.3 175798.45 757.72843 5.5944018 438.87108 -361.40519 0.12063069 0.0023903754 -0.013162922 0.012840231 -0.56841667 0.012089713 1860390.9 133.90722 300.90325

900 2954085.4 175544.46 757.60448 5.59443 438.87247 -310.769 0.11565299 0.00030602012 -0.021493001 -0.011467919 -0.59676705 -0.011173904 1860101.8 133.90167 300.46852

1000 2953893.7 175720.19 757.47719 5.5944632 438.87419 -445.52626 0.11254031 -0.029688914 0.052577452 0.011672204 -0.57303913 -0.025150062 1859807.6 133.89593 300.76929

1100 2954306.6 175305.12 757.34955 5.5945019 438.87646 -517.88655 0.1686761 -0.0043869457 -0.006864591 0.009894795 -0.5953897 -0.015985881 1859516.7 133.89015 300.05885

1200 2954644.6 174968.99 757.22337 5.594545 438.87925 -362.23289 0.10294666 0.016595127 -0.0094320432 -0.013803957 -0.59998599 -0.0095153186 1859233 133.88435 299.48351

1300 2954019.1 175579.64 757.10042 5.594597 438.88241 -301.98628 0.1032435 -0.0040662279 -0.0073809904 0.011749339 -0.58754865 0.0015912576 1858961.8 133.87864 300.52873

1400 2954396.9 175181.68 756.98184 5.5946498 438.88549 -618.14532 0.15872523 -0.0030573413 0.032232839 0.020230284 -0.61281435 -0.021091195 1858701.2 133.87301 299.84757

1500 2954518 175049 756.86728 5.5947055 438.88859 -472.12063 0.14702571 0.0057599608 -0.0092728044 0.0050096737 -0.60346713 0.004560782 1858451.6 133.86743 299.62047

1600 2954119.4 175419.21 756.75511 5.594764 438.89187 -312.09845 0.14020724 -0.054235566 0.0088984548 0.012396213 -0.57188598 0.029959382 1858209.5 133.86189 300.25413

1700 2953838.8 175683.37 756.6458 5.5948321 438.89558 -169.85443 0.10804185 -0.038022105 -0.018388247 -0.001194248 -0.5900803 0.0043512595 1857979.4 133.85645 300.70628

1800 2954227.7 175296.47 756.53953 5.5949086 438.90024 -396.75519 0.1386793 -0.0075393053 -0.010536335 -0.0064640189 -0.61931099 -0.011910746 1857763.6 133.85102 300.04404

1900 2953921.8 175567.02 756.436 5.5949897 438.90508 -261.86113 0.11006408 0.0034160361 -0.033880878 0.020699929 -0.57205832 -0.026977718 1857556.7 133.84563 300.50713

2000 2953954.7 175533.98 756.33559 5.5950745 438.91028 12.30174 0.092534779 -0.059361626 -0.036912574 0.0048311984 -0.58512894 0.0033562472 1857360.3 133.84034 300.45058

2100 2953942.9 175537.95 756.23668 5.5951652 438.91567 -188.99331 0.081875382 -0.020958837 -0.0034673022 -0.051216845 -0.5705078 0.0062238506 1857170.3 133.83495 300.45738

2200 2953546 175900.17 756.13947 5.5952594 438.92112 -268.05152 0.10580717 -0.0094804938 -0.014845722 -0.0081496927 -0.58000123 -0.021426313 1856985.9 133.82962 301.07735

2300 2954095.8 175346.63 756.04403 5.5953566 438.9268 -405.96553 0.12382069 0.012869439 -0.013286753 0.03025316 -0.58676961 -0.018979137 1856807.8 133.82441 300.1299

2400 2953683.9 175731.86 755.94814 5.5954617 438.93296 -94.426367 0.058239099 -0.016287436 -0.013248408 -0.021270793 -0.59270955 -0.0051872851 1856633.2 133.81914 300.78927

2500 2954120.2 175292.31 755.85178 5.5955687 438.93952 -69.403557 0.070324696 -0.030119638 -0.019108111 -0.0037870507 -0.58435604 0.0086068066 1856459.8 133.81376 300.03693

2600 2953950.8 175437.7 755.75674 5.5956769 438.94591 -319.17027 0.10802612 -0.017443465 0.0064371284 0.018879556 -0.61509576 -0.001281716 1856289.3 133.80847 300.28578

2700 2954215.4 175156.08 755.66207 5.5957809 438.95186 -282.4958 0.064531442 0.013792282 0.0075479353 -0.01431586 -0.58229432 0.025728427 1856116.4 133.80309 299.80374

2800 2954066.5 175283.29 755.56794 5.5958884 438.95828 152.28561 0.055623516 -0.034876782 -0.067037752 0.019313385 -0.58000906 0.030263317 1855948 133.7977 300.02149

2900 2953747.3 175583.68 755.47459 5.5960017 438.9652 -262.19937 0.10122893 -0.033328852 0.011801973 0.012824474 -0.62156934 0.011305169 1855785.6 133.79237 300.53564

3000 2953751.1 175575.09 755.38201 5.5961185 438.97223 -334.75392 0.10050874 0.0015420251 -0.00029393892 -0.032631261 -0.59006374 0.032774696 1855626.6 133.78713 300.52095

3100 2953551.6 175746.19 755.29019 5.5962416 438.97969 11.146597 0.088236357 -0.019432281 -0.072192363 0.010885473 -0.57940979 0.0019293222 1855473.4 133.78189 300.81381

3200 2953790 175487.49 755.19891 5.596369 438.98747 84.824282 0.062349994 -0.05293045 -0.035204005 -0.0019135452 -0.57617024 0.0076699931 1855324.3 133.77659 300.371

3300 2953340.9 175919.21 755.10968 5.596502 438.99545 -36.893331 0.061341542 -0.024539791 -0.025587101 0.0088937398 -0.59725646 -0.0077692656 1855182.9 133.77146 301.10996

3400 2953679 175570.59 755.0209 5.5966338 439.00333 -202.81523 0.10001709 -0.03618116 -0.0021851727 0.023716258 -0.57511211 -0.0074539104 1855041.7 133.76623 300.51324

3500 2953815.6 175426.4 754.93254 5.5967743 439.01122 -209.53338 0.065433535 -0.012130651 0.010390024 -0.019652419 -0.60641403 0.0045864559 1854904.5 133.76102 300.26643

3600 2953346.1 175869.18 754.84519 5.5969157 439.01868 -347.60795 0.091471483 -0.0031265311 0.017319173 -0.012135446 -0.58468187 0.0093830224 1854768.2 133.7559 301.02432

3700 2953851.8 175335.84 754.75829 5.5970536 439.02556 -143.07695 0.097647833 -0.041422492 -0.012733525 0.017000141 -0.59071908 0.015133362 1854629.5 133.75076 300.11143

3800 2953719.4 175468.85 754.67317 5.5971975 439.03245 -141.89789 0.072184234 3.4343244e-05 -0.029085166 0.032204036 -0.59138095 -0.0072666205 1854497.1 133.74573 300.33909

3900 2953524.6 175638.64 754.58923 5.5973421 439.03915 -318.49232 0.093465106 0.0093420185 -0.005993421 0.0027652262 -0.60063647 -0.022916229 1854367.1 133.74081 300.62972

4000 2953536.5 175617.59 754.50611 5.5974939 439.04627 -324.47701 0.10035907 -0.0086031399 0.0068769646 0.0050349535 -0.60240087 -0.012478416 1854243.1 133.73593 300.59368

4100 2953180.5 175948.08 754.42379 5.597647 439.05382 -81.394728 0.035571257 -0.025236986 0.014407692 0.0041361853 -0.5610184 0.011833199 1854123.4 133.73108 301.15937

4200 2953733.6 175394.28 754.34289 5.597799 439.06136 -271.14835 0.098057049 -0.010880347 -0.0047543808 0.01088681 -0.59171843 -0.0035573049 1854006.8 133.72619 300.2114

Sincerely,
Joe