Add variational Monte Carlo (VMC) using [ForwardDiff.jl](https://github.com/JuliaDiff/ForwardDiff.jl).[DifferentiationInterface.jl](https://github.com/JuliaDiff/DifferentiationInterface.jl) is useful to define second derivative.
Add variational Monte Carlo (VMC) using ForwardDiff.jl.DifferentiationInterface.jl is useful to define second derivative.