Ground state of asymmetric tops with DMRG: Water in one dimension

We propose an approach to compute the ground state properties of collections of interacting asymmetric top molecules based on the density matrix renormalization group method. Linear chains of rigid water molecules of varying sizes and density are used to illustrate the method. A primitive computational basis of asymmetric top eigenstates with nuclear spin symmetry is used, and the many-body wave function is represented as a matrix product state. We introduce a singular value decomposition approach in order to represent general interaction potentials as matrix product operators. The method can be used to describe linear chains containing up to 50 water molecules. Properties such as the ground state energy, the von-Neumann entanglement entropy, and orientational correlation functions are computed. The effect of basis set truncation on the convergence of ground state properties is assessed. It is shown that specific intermolecular distance regions can be grouped by their von-Neumann entanglement entropy, which in turn can be associated with electric dipole-dipole alignment and hydrogen bond formation. Additionally, by assuming conservation of local spin states, we present our approach to be capable of calculating chains with different arrangements of the para and ortho spin isomers of water and demonstrate that for the water dimer.

Automated summary

We propose an approach based on the density matrix renormalization group method to compute the ground state properties of interacting asymmetric top molecules. The method is demonstrated using linear chains of water molecules of varying sizes and density. By using a computational basis of asymmetric top eigenstates and utilizing a matrix product state representation for the many-body wave function, the method is able to describe chains containing up to 50 water molecules. Various properties such as ground state energy, entanglement entropy, and orientational correlation functions are computed, and the effect of basis set truncation on convergence is assessed. We also show that different intermolecular arrangements can be calculated by assuming conservation of local spin states, highlighting the capability of our approach.