Comment on "Regularizing the MCTDH equations of motion through an optimal choice on-the-fly (i.e., spawning) of unoccupied single-particle functions" [D. Mendive-Tapia, H.-D. Meyer, J. Chem. Phys. 153, 234114 (2020)]

Abstract

The purpose of the present Comment is to point out the connection between an approach to spawning and regularization that was recently introduced by D. Mendive-Tapia and H.-D. Meyer [J. Chem. Phys. 153, 234114 (2020)] in the context of the Multiconfiguration Time-Dependent Hartree (MCTDH) method, and earlier work where adaptive variational quantum propagation based on the Local-in-Time Error (LITE) was introduced [R. Martinazzo and I. Burghardt, Phys. Rev. Lett. 124, 150601 (2020); arXiv:1907.00841 [quant-ph] (2019)]. Furthermore, we show that the LITE represents a gauge-invariant distance which provides a natural, physically sound tool for adaptive quantum dynamics.