LJ势函数单位体制
Thelj/cutstyles compute the standard 12/6 Lennard-Jones potential, given by
E二4rf(-)12 -(-)6]r < q r r c
Rc is the cutoff.
units lj
For stylelj, all quantities are unitless. Without loss of generality, LAMMPS sets the fundamental quantitiesmass, sigma, epsilon, and the Boltzmann constant = 1. The masses, distances, energies you specify aremultiples of these fundamental values・The formulas relating the reduced or unitless quantity (with anasterisk) to the same quantity with units is also given. Thus you can use the mass & sigma & epsilon valuesfor a specific material and convert the results from a unitless LJ simulation into physical quantities.
mass = mass or m •
distance = sigma, where x* 二x / sigma • time = tau, where t* = t (epsilon / m/ sigma A2)A l/2 • energy = epsilon, where E* 二E / epsilon • velocity = sigma/tau, where v* = v tau / sigma • force = epsilon/sigma, where f* 二f sigma / epsilon • torque (力矩)=epsilon, where t* = t / epsilon •temperature = reduced LJ temperature, where T* = T K b / epsilon •pressure = reduced LJ pressure, where P* 二P sigma A3 / epsilon •
•dynamic viscosity = reduced LJ viscosity, where eta* = eta sigma A3 / epsilon / tau
•charge = reduced LJ charge, where q* = q / (4 pi permO sigma epsilon)A1/2
•dipole = reduced LJ dipole, moment where *mu 二mu / (4 pi permO sigma A3 epsilon)A l/2
•electric field = force/charge, where E* 二E (4 pi permO sigma epsilon)A l/2 sigma / epsilon
•density = mass/volume, where rho* = rho sigma A dim
Lamps中的LJ单位问题
LJ单位
mass： =2.43x10 *kg,即［mass 相当于2-43x10 8kg
sigma：=lxl0_5m ,即1 sigma 相当于lxl(T5m
epsilon：=8.41xlO'l3N-m ,即1 epsilon 相当于8.41xlO_13N m
那么根据manual里面的dipole的解释，即：
dipole = reduced LJ dipole, moment where *mu = mu / (4 pi permO sigma A3 epsilon)A l/2
所以1 dipole 相当于(4 pi permO sigma A3 epsilon)A l/2
即.y]47rx/?(?n/7Ox(lxlO~5m)3x8.41xlO_13N m
根据您的解释，这里的pennO应该也是一个约化单位，即permO=l,但在计算的过程中要转化成实际单位，故应该此处的
permO = --- ---- 7
4^X10-7N/A2,也只有这样，dipole的量纲分析才正确。那么：
(4 兀 X / 疋厂加0x(lxl(r'm)'x8.41xl0"Nm
density, typically written as rho*. LAMMPS converts this value into the multiplicative factor via the formula n factor A dim = rho/rho*", where rho =N/V with V = the volume of the lattice unit cell and N = the number of basis atoms in the unit cell (described below), and dim = 2 or 3 for the dimensionality of the simulation. Effectively, this means that if LJ particles of size sigma = 1.0 are used in the simulation, the lattice of particles will be at the desired reduced density.
对于lj单元，scale是Lennard-Jones折算密度，典型写为rho*。Lammps通过公式”factoMdim = rho/rho*”将这个值转变为倍增因子。Rho二N/V, 晶格单元的体积，n=晶胞中基本原子的数量，dim根据
模拟的维度等于2或者3。实际上这表明如果在模拟中使用的lj粒了的sigma=1.0,那么晶格中的粒子将会有预期的折算密度。
Thermo 输!1J 量
The content and format of what is printed is controlled by the thermo_styleand thermo_modifycommands.
thermo_style
Default: thermo_style one
Styleoneprints a one-line summary of thermodynamic info that is the equivalent of H thermo_style customstep temp epair emol etotal press". The
