Quantum dynamics with Bohmian trajectories: energy conserving approximation to the quantum potential

The Schrِdinger equation can be solved in terms of quantum trajectories evolving under the influence of quantum potential. We present a method of computing the quantum potential by approximating the non-classical component of the momentum operator, such that the total energy of a closed system is conserved. A case of special interest is linearized quantum force with analytical parameters and correct average value. This method is computationally cheap and exact for locally quadratic potentials. We illustrate its efficiency and accuracy by computing the photodissociation spectrum of ICN and the wavepacket transition probability for H3 in two dimensions.