Antisymmetry in the quantum Monte Carlo method without a trial function

The problem of antisymmetry in the quantum Monte Carlo method is handled by a technique able to build up mobile nodal surfaces, self-adapting to the signed psip distribution. We define a function A as a sum of Gaussians, each one centered on a psip and with its own sign. This sum is extended to the psips obtained by antisymmetrization of those actually used in the random walk. The A function defines the nodal surfaces in the full (3N-1) -dimensional space and not only in the (3N—3)-dimensional subspace obtained by the antisymmetry definition. Calculations are presented for the 2P state of the hydrogen atom and for the triplet state of the hydrogen molecule.