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LAMMPS讲解41-氯化钠NaCl熔盐粘度和扩散系数模拟本例发布氯化钠NaCl熔盐粘度和扩散系数模拟。力场参数取自文献Solid–solid phase equilibria in the NaCl-KCl system。粘度通过Green-Kubo关系计算，还可以通过其他方法获得更为准确的粘度。扩散系数通过均方位移计算。在本例in文件的基础上还可以计算热导率，RDF等其他参数。
in文件
units real dimension 3 boundary p p p neighbor 3.0 bin neigh_modify every 1 delay 0 check yes atom_style charge pair_style born/coul/long 10.0 8.0 kspace_style pppm 10e-4
region box block -40 40 -40 40 -40 40 units box create_box 2 box
lattice sc 4 region part1 block -40 40 -40 40 -40 -4.0 units box create_atoms 1 region part1
lattice sc 4 region part2 block -40 40 -40 40 0.0 40 units box create_atoms 2 region part2 #Na = 1 Cl = 2
pair_coeff 1 1 6.0772 0.3167 2.340 24.164 11.5076 pair_coeff 1 2 4.8617 0.3167 2.755 161.1 199.93 pair_coeff 2 2 3.6462 0.3267 3.170 1729.64 3473.65
set type 1 charge 1.0 set type 2 charge -1.0
mass 1 22.9898 mass 2 35.45
dump mydump all atom 1000 atom.lammpstrj
minimize 0.0 1.0e-8 1000 100000
timestep 1.0 thermo 100 thermo_style custom step temp density thermo_modify flush yes velocity all create 1200 5645354 loop local dist gaussian
fix fxnpt all npt temp 1200 1200 100 iso 100 100 1000
run 100000
unfix fxnpt
fix fxnpt all npt temp 1200 1200 100 iso 1.0 1.0 1000
run 100000
unfix fxnpt
variable dt equal 1.0 variable kB equal 1.3806504e-23 variable g_mol2kg equal 1.0e-3/6.02214e23 variable A2m equal 1.0e-10 variable fs2s equal 1.0e-15 variable atm2pa equal 1.01325e5 variable convert_eta equal ${atm2pa}*${atm2pa}*${A2m}*${A2m}*${A2m}*${fs2s} variable kCal2J equal 4186.0/6.02214e23 variable convert_kappa equal ${kCal2J}/${fs2s}/${A2m} variable convert_rho equal 1000
reset_timestep 0 variable p equal 2000 # correlation length variable s equal 5 # sample interval variable d equal $p*$s # dump interval thermo $d variable pxy equal pxy variable pxx equal pxx-press variable pxz equal pxz variable pzz equal pzz-press variable pyz equal pyz variable pyy equal pyy-press fix SS all ave/correlate $s $p $d v_pxy v_pxx v_pxz v_pzz v_pyz v_pyy type auto file profile.gk ave running
variable scale equal 1.0/1200/${kB}*vol*$s*dt variable diagfac equal 2-2/3 variable vxy equal trap(f_SS[3])*${scale}*${convert_eta} variable vxx equal trap(f_SS[4])*${scale}/${diagfac}*${convert_eta} variable vxz equal trap(f_SS[5])*${scale}*${convert_eta} variable vzz equal trap(f_SS[6])*${scale}/${diagfac}*${convert_eta} variable vyz equal trap(f_SS[7])*${scale}*${convert_eta} variable vyy equal trap(f_SS[8])*${scale}/${diagfac}*${convert_eta}
fix fxnvt all nvt temp 1200 1200 100.0
thermo_style custom step temp press pxy pxz pyz v_vxy v_vxx v_vxz v_vzz v_vyz v_vyy thermo_modify flush yes
run 100000
unfix SS reset_timestep 0
compute msd all msd com yes variable twopoint equal c_msd[4]/6/(step*dt+1.0e-6) fix 9 all vector 10 c_msd[4] variable fitslope equal slope(f_9)/6/(10*dt)
thermo 1000 thermo_style custom step temp c_msd[4] v_twopoint v_fitslope thermo_modify flush yes
run 100000
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