molecular_dynamics.jl

# Credit: leandromartinez98@https://discourse.julialang.org
# This code is adapted from https://discourse.julialang.org/t/seven-lines-of-julia-examples-sought/50416/41
# Perform a particle simulation with periodic boundary conditions, a langevin thermostat, and a quadratic potential between the particles, and produce an animation in 15 lines.
using Plots ; ENV["GKSwstype"]="nul"

const N, τ, Δt, λ, T, k = 100, 1000, 0.01, 1e-3, 0.26, 1e-6
const x, v, f = -0.5 .+ rand(3,N), -0.01 .+ 0.02*randn(3,N), zeros(3,N)

wrap(x,y) = (x-y) > 0.5 ? (x-y)-1 : ( (x-y) < -0.5 ? (x-y)+1 : (x-y) )

anim = @animate for t in 1:τ 
  f .= 0
  for i in 1:N-1, j in i+1:N 
    f[:,i] .+= wrap.(x[:,i],x[:,j]) .- λ .* v[:,i]
    f[:,j] .+= wrap.(x[:,j],x[:,i]) .- λ .* v[:,j]
  end 
  x .= wrap.(x .+ v*Δt .+ (f/2)*Δt^2,zeros(3))
  v .= v .+ f*Δt .+ sqrt.(2*λ*k*T*Δt)*randn()
  scatter(x[1,:],x[2,:],x[3,:],label="",lims=(-0.5,0.5),aspect_ratio=1,framestyle=:box)
end

gif(anim,"anim.gif",fps=10)