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)]

TL;DR

This paper discusses the connection between recent spawning and regularization methods in the MCTDH approach and earlier adaptive quantum propagation techniques, highlighting the physical soundness of the LITE measure.

Contribution

It reveals the relationship between the recent MCTDH regularization approach and the LITE-based adaptive quantum propagation, emphasizing gauge invariance and physical interpretability.

Findings

LITE is a gauge-invariant distance measure.

The approach unifies recent and earlier adaptive quantum dynamics methods.

LITE provides a physically meaningful tool for quantum state propagation.

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.