PaPIM is a code for calculation of equilibrated system properties (observables). Some properties can be directly obtained from the distribution function of the system, while properties that depends on the exact dynamics of the system, such as the structure factor, [Mon2] infrared spectrum [Beu] or reaction rates, can be obtained from the evolution of appropriate time correlation functions. PaPIM samples either the quantum (Wigner) or classical (Boltzmann) density functions and computes approximate quantum and classical correlation functions.

The code is highly parallelized and suitable for use on large HPC machines. The code’s modular structure enables an easy update/change of any of its modules. Furthermore the coded functionalities can be used independently of each other. The code is specifically design with simplicity and readability in mind to enable any user to easily implement its own functionalities. The code has been extensively used for the calculation of the infrared spectrum of the \text{CH}_{5}^{+} cation in gas phase, while recently new calculations on the water dimer, and protonated water dimer systems were started.