where r is either +1 or -1, chosen at random. All points sampled with this procedure have the same harmonic-oscillator energy E given by eq (22). Nevertheless, when the potential energy of the sampled geometry is determined with the quantum-chemical method, anharmonic effects are introduced, and the energy distribution broadens again. To ensure a sharp distribution around E , all Cartesian velocities can be rescaled as (26) where Kn and EJ,n are the kinetic and quantum-chemical potential energies computed at the sampled geometry and momentum n. J is the electronic state that is being sampled, usually the ground state (J = 1).