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Hi lammps users,
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im trying to calculate the equation of state (EOS) (T=0) for different structures eg. BCC, FCC, HCP. Please find the script below. I'm using fix deform and storing Etotal/atom and VOL/Vo.
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The plot of (E vs V) I believe make sence because the minimum of energy is equal to the Ecohesive. Foe example lets use Cu EAM Potential Mishin Cu EAM1 PRB(2001)63:224106
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I'm also trying to find Enthalpy vs Pressure for different phases. I'm trying to Compare FCC enthalpy vc HCP enthalpy at T=0 .
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Unfourtounately my script is wrong. In order to compare two data sets, the data sets should be of same lenght and the values space evenly i.e Equal values of Pressure P correspong to different values of Enthalpy "H"
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Example ENTHALPHY VS P (BCC) P=10 , H=1 ENTHALPHY VS P (HCP) P=10 , H=23 (values are spaces evenly in pressure)
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Can someone please tell me how to find Enthalpy vs Pressure (T=0) for different Phases using Lammps ?
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Any information will be grealy appreciate
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Thanks alot for your help and advise
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Oscar Guerrero
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```
# ---------- Initialize Simulation ---------------------
clear
units metal
dimension 3
boundary p p p
atom_style atomic
atom_modify map array
# ---------- define variables -------------------------------
timestep 0.005
# ---------- Create Atoms ------------------------------------
lattice bcc 3.615 origin 0.0 0.0 0.0 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
# lattice fcc 3.615 origin 0.0 0.0 0.0 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
# lattice hcp 3.615 origin 0.0 0.0 0.0 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
region box block 0 5 0 5 0 5 units lattice
create_box 1 box
create_atoms 1 box
# ---------- Define Interatomic Potential ---------------------
pair_style eam/alloy
pair_coeff * * Cu_mishin1.eam.alloy Cu
# ---------- Define Settings ----------------------------------
compute eng all pe/atom
compute kiene all ke/atom
compute pre all stress/atom
compute eatoms all reduce sum c_eng
# ---------- Print Atoms ----------------------------------
reset_timestep 0
dump 1 all cfg 2 lattice.dump.*.cfg id type xs ys zs
run 1
undump 1
# ---------- FIND MINIMUM ENERGY LEVEL -------------------------
reset_timestep 0
fix 1 all box/relax iso 0.0 vmax 0.001
thermo 0
thermo_style custom step pe lx ly lz vol press pxx pyy pzz c_eatoms
min_style cg
minimize 1e-25 1e-25 5000 10000
unfix 1
#--------------STORE TEMPORARY VARIABLES ----------------------------
# Store final volume/atom for further calculations
variable tmp equal "vol/count(all)"
variable V0 equal ${tmp}
print "Volume per atom, V0: ${V0}"
# Store final length for further calculations
variable tmp equal "lx"
variable L0 equal ${tmp}
print "Initial Length, L0: ${L0}"
# ---------- DEFORMATION STEPS ARE HERE ----------------------------------
reset_timestep 0
# RUN SIMULATION AT 0K
fix 1 all deform 1 x erate -0.10 remap x
# ---------- FIND EQUATION OF STATE ------------------------------------
thermo 0
thermo_style custom step etotal enthalpy lx ly lz vol press pxx pyy pzz temp
variable natoms equal "count(all)" # NUMBER ATOMS
variable H equal "enthalpy/v_natoms" # ENTHALPY
variable strain equal "-(lx - v_L0)/v_L0" # STRAIN
variable shear equal "0.5*(pxx - 0.5*(pyy + pzz))/10000" # SHEAR CALCULATION
variable out1 equal "(vol/v_natoms)/v_V0" # VOLUME PER ATOM
variable out2 equal "etotal/v_natoms" # TOTAL ENERGY PER/ATOM
variable out3 equal "pxx/10000" # PRESSURE PXX (GPA UNITS)
variable out4 equal "pyy/10000" # PRESSURE PYY (GPA UNITS)
variable out5 equal "pzz/10000" # PRESSURE PZZ (GPA UNITS)
variable out6 equal "press/10000" # TENSOR PRESSURE (GPA UNITS)
variable out7 equal "temp" # TEMPERATURE
variable out8 equal "lx" # lx
variable out9 equal "ly" # ly
variable out10 equal "lz" # lz
fix def1 all print 2 "${strain} ${shear}" file shear.dat screen no
fix def2 all print 2 "${out1} ${out2} ${out3} ${out4} ${out5} ${out6} ${out7} ${out8} ${out9} ${out10} ${H} " file eos.dat screen no
fix def3 all print 2 "${out6} ${H} " file enthalpy.dat screen no
run 1200
unfix 1
unfix def1
unfix def2
unfix def3
# SIMULATION DONE
clear
print "creo ya esta =)"
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