The DMC method is based on the observation that the Schrodinger
equation in imaginary time (),

(5) 
is a diffusion equation plus a branching/annihilation term given by the
potential. If the parameter is tuned to the groundstate energy
the trial wavefunction is projected to the ground state of
the Hamiltonian. The antisymmetric nature of the electronic
wavefunction poses serious problems for the numerical solution of Eq
(). A way out of to this difficulty is to introduce the
so called fixednode approximation, in which a modification of Eq
() is used, that projects the wavefunction onto the ground
state wavefunction which has the same nodal surface of a trial
wavefunction. Practical computations show that this is a very good
approximation.