LAMMPS中的GCMC(巨正则蒙特卡洛)

谈谈LAMMPS中的GCMC(巨正则蒙特卡洛)

Example :fix ID group-ID gcmc N X M type seed T mu displace keyword values
N:每N步进行一次MC操作,每次操作进行 X 次的交换和 M 次的移动和旋转;
type: 原子type;
Seed:随机数种子;
T:温度;
Mu:化学势;
Displace:最大平移距离;(提前设置一个量,防止移动太远)
Keyword : {:分子模板 ;:MC移动的区域 ;:分子最大旋转角度 ;: 气体压力(与体系耦合的大气体浴); <full_energy>:Metropolis比较的时候,计算full energy判断 (复杂体系);<intra_energy>:需要交掉的分子内势能(rigid or shake, …dont worry…) ; :新加入分子的group ; <overlap_cutoff>: overlap拒接受的最大距离}。
在这里插入图片描述

上面是简单的命令介绍,打开LAMMPS的EXAMPLE看看里面有几个case可以学习。

# GCMC for LJ simple fluid, no dynamics
# T = 2.0
# rho ~ 0.5
# p ~ 1.5
# mu_ex ~ 0.0
# comparable to Frenkel and Smit GCMC Case Study, Figure 5.8 

# variables modifiable using -var command line switch

variable        mu index -1.25
variable        temp index 2.0
variable	disp index 1.0
variable        lbox index 5.0

# global model settings

units           lj
atom_style      atomic
pair_style      lj/cut 3.0 
pair_modify	tail no # turn of to avoid triggering full_energy

# box

region		box block 0 ${lbox} 0 ${lbox} 0 ${lbox}
create_box	1 box

# lj parameters

pair_coeff	* * 1.0 1.0
mass		* 1.0

# we recommend setting up a dedicated group for gcmc

group		gcmcgroup type 1

# gcmc

fix              mygcmc gcmcgroup gcmc 1 100 100 1 29494 ${temp} ${mu} ${disp}

# atom count

variable 	    type1 atom "type==1"  
group 		     type1 dynamic gcmcgroup var type1  ## 设置动态group 粒子数可以变化
variable        n1 equal count(type1)   ###统计粒子数

# averaging

variable	   rho equal density
variable	   p equal press
variable	   nugget equal 1.0e-8
variable      lambda equal 1.0
variable     	muex equal ${mu}-${temp}*ln(density*${lambda}+${nugget})
fix 		        ave all ave/time 10 100 1000 v_rho v_p v_muex v_n1 ave one file rho_vs_p.dat
variable	    rhoav equal f_ave[1]
variable	    pav equal f_ave[2]
variable	    muexav equal f_ave[3]
variable	    n1av equal f_ave[4]

# output

variable	tacc equal f_mygcmc[2]/(f_mygcmc[1]+${nugget})
variable	iacc equal f_mygcmc[4]/(f_mygcmc[3]+${nugget})
variable	dacc equal f_mygcmc[6]/(f_mygcmc[5]+${nugget})
### particle number is not a contant 
compute_modify  thermo_temp dynamic yes
thermo_style    custom step temp press pe ke density atoms v_iacc v_dacc v_tacc v_rhoav v_pav v_muexav v_n1av
thermo          1000

run             10000

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转载自blog.csdn.net/qq_43689832/article/details/104434168

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