Abstract:
This research aims to advance the quantum dynamics simulation of van der Waals molec
ular clusters, including H2O–H2O, H2O–HCN, and N2O–CO, which are formed with abundant molecules in the interstellar medium (ISM) such H2O and CO. While these sys
tems have traditionally been studied through classical methods, the full quantum approach
using the Multi-Configuration Time-Dependent Hartree (MCTDH) method was chosen to
address challenges related to dimensionality. A critical first step in this approach is the
accurate representation of the Potential Energy Surface (PES), as it underpins all subse
quent calculations. Although previous studies have characterized some properties of these
clusters, this work provides comprehensive rovibrational state calculations and initiates
collision simulations for the water dimer. Achieving convergence, however, has proven
challenging, as it is highly sensitive to the size of the primitive basis set and the num
ber of single-particle functions (SPFs) utilized in flux calculations for computing inelastic
cross sections and rate coefficients. Spectroscopic calculations were performed using the
Block Improved Relaxation procedure from the Heidelberg MCTDH package, allowing ex
traction of transition frequencies and rotational constants. The zero-point energy (ZPE)
and intermolecular vibrational frequencies obtained from these simulations align well with
prior ab initio studies, while the transition frequencies and rotational constants show good
agreement with experimental data.
