Dear all,
I want to study the effect of pressure enhancement on the thermal properties of an epoxy system. I was thinking that with using fix NPT, I would be able to specified a desired pressure for my system and running fix NPT for around 2 ns leads that system’s temperature, volume, and density reach to a constant value, therefore, I assume that my system is well equilibrated. The thing is as I extract pressure tensor in the perpendicular directions (Pxx,Pyy,Pzz), the values are far from the pressure that I have specified and I am wondering how these numbers could be related to the pressure specified by me.
I have attached part of my input file and also the extracted pressure tensor here.
I would be really thankful, if someone tell me what I am doing wrong here and how can I control pressure properly in my system.
Any comment would be highly appreciated.
################################# INPUT File in Real Unit #####################
read_restart restart.EM-NPT1-700ps-NPT2-1300ps
###------------------------------------------------- pair potentials-----------------------------------------------------------------------######
kspace_style ewald 1e-4
pair_style hybrid/overlay lj/class2/coul/long 10.0 tersoff
pair_coef…
neighbor 2.260777 bin
pair_modify shift no tail yes
special_bonds lj/coul 0.0 0.0 0.5
##########-------------------------------------------------------------Variables definition--------------------------------------------##############
variable t equal 0.5
variable tdamp equal $t100
variable pdamp equal $t1000
variable PXX equal “pxx”
variable PYY equal “pyy”
variable PZZ equal “pzz”
timestep $t
##############################-----------------------------------Equilibration-------------------#####################################################
thermo 1000
thermo_style custom elapsed temp ke pe lx ly lz density press
thermo_modify lost warn
group polymer type 1:9
fix system_properties polymer ave/time 1000 10 10000 v_PXX v_PYY v_PZZ file pressure.dat
###############################----------------------------------------NPT 500 ps--------------------------------#############################################
fix 1 polymer npt temp 300 300 {tdamp} iso 2 5 {pdamp} drag 2
run 500000
unfix 1
fix 1 polymer npt temp 300 300 {tdamp} iso 5 5 {pdamp} drag 2
run 500000
unfix 1
write_restart restart.EM-NPT1-700-NPT2-1300-NPT3-500
Kind regards,
Shahin Mohammadnejad
pressure.dat (3.33 KB)