Estimation of the anharmonic quantum density of states in large systems

We present a mixed quantum/classical model which allows an estimation of the quantum density of vibrational states in large anharmonic systems. The construction of the model is based on the modification of the harmonic quantum density of states by using the evolution of the classical anharmonic mean energy as a function of temperature, computed from a classical canonical Nosé simulation. The validity of the assumptions proposed in this model has been tested for two 1-D and 2-D model systems for which exact quantum calculations are feasible.