Optimized basis sets for DMRG calculations of quantum chains of rotating water molecules

In this contribution, we employ a density matrix-based optimization procedure to obtain customized basis functions to describe chains of rotating water molecules in interaction regimes associated with different intermolecular distances. This procedure is shown to yield a very compact basis with a clear truncation criterion based on the population of the single particle basis functions. For the water trimer, we discuss the convergence behavior of several properties and show it to be superior when compared to an energy-based truncated basis. It is demonstrated that the optimized basis reduces the necessary number of basis functions by at least an order of magnitude. Finally, the optimization procedure is employed to study larger chains of up to ten water molecules. The formation of hydrogen bonds as well as its impact on the net polarization of the chain is discussed.

Automated summary

In this study, a density matrix-based optimization procedure is used to generate customized basis functions for describing rotating water molecule chains at different intermolecular distances. The procedure provides a compact basis with a clear truncation criterion based on the population of single particle basis functions. For the water trimer, the convergence behavior of various properties is discussed and shown to be superior to an energy-based truncated basis. It is demonstrated that the optimized basis reduces the required number of basis functions by at least an order of magnitude. Finally, the optimization procedure is applied to larger chains of up to ten water molecules, investigating the formation of hydrogen bonds and their impact on the net polarization of the chain.