arXiv subjects

Ludwik Adamowicz

Publications and source records attributed to Ludwik Adamowicz.

7 recordsLinked to original sources

arXiv2026

Rothe's Method for Quantum Dynamics in Atoms and Molecules with Gaussian Wavepackets

Capable of capturing both bound and continuum quantum dynamics, Gaussian wavepackets are highly attractive basis functions for simulating laser-driven processes in atoms and molecules. Unfortunately, fully flexible Gaussian wavepackets are exceedingly challenging to propagate in a numerically stable manner within the framework of conventional time-dependent variational principles. In this chapter, we discuss the sources of the numerical issues and review an alternative approach, Rothe's method, that offers a route to improved numerical stability. Recent proof-of-concept simulations based on Rothe's method indicate that Gaussian wavepackets provide results on par with highly accurate grid-based methods for both electronic and rovibrational quantum dynamics, including ultrafast nonlinear processes that involve the continuum such as high-harmonic generation. Remarkably few Gaussian wavepackets are needed to achieve the high accuracy of grid-based approaches, indicating that further algorithmic developments and efficient implementations may enable efficient simulations of not only electronic and rovibrational phenomena but also fully coupled electronic-nuclear quantum dynamics with significantly reduced memory demands. We also point out remaining practical challenges, including matrix elements of the squared Hamiltonian and the treatment of Coulomb cusps.

physics.chem-ph↗

arXiv2025

Binding of native DNA to MoS$_{2}$ nanoflakes: the role of defects and edge atoms of MoS$_{2}$ nanostructures in their biofunctionalization

In this work, the binding of native DNA to MoS$_{2}$ nanoflakes (FLs) was studied by using UV-visible absorption spectroscopy, thermal denaturation method, transmission electron microscopy (TEM), temperature-dependent dynamic light scattering (DLS), and the DFT computational-chemistry method. Analysis of the experimental data: TEM images and thermal denaturation measurements showed the binding of the biopolymer with MoS$_{2}$ FLs. An increase in the melting temperature of DNA and a decrease in the hyperchromic coefficient at binding with MoS$_{2}$ FLs indicates the formation of the DNA:MoS$_{2}$ FL nanoassemblies due primarily to the covalent interaction of the oxygen atoms of the phosphate groups of DNA with the MoS$_{2}$ FLs. Possible complexes of a nucleotide fragment (ribose-phosphate group) with MoS$_{2}$ nanolayer are considered and calculated employing the DFT method. Different structures of these complexes are optimized and the interaction energies between components are determined. Special attention in calculations is focused on the binding of this nucleotide fragment with Mo atoms located at the edge of the MoS$_{2}$ nanolayer and with point structural defects of the MoS$_{2}$ surface containing the S vacancy. Based on this calculation and experimental observation, a mechanism of binding of native DNA to MoS$_{2}$ FLs has been proposed, in which their conjugation begins with point contacts of DNA phosphate groups with Mo atoms (at the edge or/and in defects) through the formation of a strong coordination bond. The results indicate the critical role of defects and edge atoms of MoS$_{2}$ FLs in their biofunctionalization.

physics.bio-ph↗

arXiv2025

Rothe Time Propagation for Coupled Electronic and Rovibrational Quantum Dynamics

When time-propagating a wave packet representing a molecular system interacting with strong attosecond laser pulses, one needs to use an approach that is capable of describing intricate coupled electronic-nuclear events that require departure from the conventional adiabatic Born-Oppenheimer (BO) approximation. Hence, the propagation should be carried out simultaneously for the electrons and nuclei, treating both particle types on an equal footing \emph{without} invoking the BO approximation. In such calculations, in order to achieve high accuracy, the wave packet needs to be expanded in basis functions that explicitly depend on interparticle distances, such as all-particle explicitly correlated Gaussians (ECGs). In our previous work, we employed basis sets consisting of ECGs with optimizable complex exponential parameters to fit time-dependent wave functions obtained from grid-based propagations of two model systems: a nucleus in a Morse potential and an electron in a central-field Coulomb-like potential, subjected to intense laser pulses. In this work, we present a proof-of-principle study of the time propagation of linear combinations of ECGs for these two models using Rothe's method. It is shown that the approach very closely reproduce the virtually exact results of grid-based propagation for both systems. This provides further evidence that ECGs constitute a viable alternative to purely grid-based simulations of coupled nuclear-electronic dynamics driven by intense laser pulses.

physics.chem-ph↗

arXiv2024

Gaussians for Electronic and Rovibrational Quantum Dynamics

The assumptions underpinning the adiabatic Born-Oppenheimer (BO) approximation are broken for molecules interacting with attosecond laser pulses, which generate complicated coupled electronic-nuclear wavepackets that generally will have components of electronic and dissociation continua as well as bound-state contributions. The conceptually most straightforward way to overcome this challenge is to treat the electronic and nuclear degrees of freedom on equal quantum-mechanical footing by not invoking the BO approximation at all. Explicitly correlated Gaussian (ECG) basis functions have proved successful for non-BO calculations of stationary molecular states and energies, reproducing rovibrational absorption spectra with very high accuracy. In this paper, we present a proof-of-principle study of the ability of fully flexible ECGs (FFECGs) to capture the intricate electronic and rovibrational dynamics generated by short, high-intensity laser pulses. By fitting linear combinations of FFECGs to accurate wave function histories obtained on a large real-space grid for a regularized 2D model of the hydrogen atom and for the 2D Morse potential we demonstrate that FFECGs provide a very compact description of laser-driven electronic and rovibrational dynamics.

physics.chem-ph↗

arXiv2022

No need for a grid: Adaptive fully-flexible gaussians for the time-dependent Schr\"odinger equation

Linear combinations of complex gaussian functions, where the linear and nonlinear parameters are allowed to vary, are shown to provide an extremely flexible and effective approach for solving the time-dependent Schr\"odinger equation in one spatial dimension. The use of flexible basis sets has been proven notoriously hard within the systematics of the Dirac--Frenkel variational principle. In this work we present an alternative time-propagation scheme that de-emphasizes optimal parameter evolution but directly targets residual minimization via the method of Rothe's method, also called the method of vertical time layers. We test the scheme using a simple model system mimicking an atom subjected to an extreme laser pulse. Such a pulse produces complicated ionization dynamics of the system. The scheme is shown to perform very well on this model and notably does not rely on a computational grid. Only a handful of gaussian functions are needed to achieve an accuracy on par with a high-resolution, grid-based solver. This paves the way for accurate and affordable solution of the time-dependent Schr\"odinger equation for atoms and molecules within and beyond the Born--Oppenheimer approximation.

quant-ph↗

arXiv2022

Laser-induced dynamic alignment of the HD molecule without the Born-Oppenheimer approximation

Laser-induced molecular alignment is well understood within the framework of the Born-Oppenheimer (BO) approximation Without the BO approximation, however, the concept of molecular structure is lost, making alignment hard to define precisely. In this work, we demonstrate the emergence of alignment from the first-ever non-BO quantum dynamics simulations, using the HD molecule exposed to ultrashort laser pulses as a few-body test case We extract the degree of alignment from the non-BO wave function by means of an operator expressed in terms of pseudo-proton coordinates that mimics the BO-based definition of alignment The only essential approximation, in addition to the semiclassical electric-dipole approximation for the matter-field interaction, is the choice of time-independent explicitly correlated Gaussian basis functions. We use a variational, electric-field-dependent basis-set construction procedure, which allows us to keep the basis-set dimension low whilst capturing the main effects of electric polarization on the nuclear and electronic degrees of freedom. The basis-set construction procedure is validated by comparing with virtually exact grid-based simulations for two one-dimensional model systems: laser-driven electron dynamics in a soft attractive Coulomb potential and nuclear rovibrational dynamics in a Morse potential.

physics.chem-ph↗

arXiv2015

Visible line intensities of the triatomic hydrogen ion from experiment and theory

The visible spectrum of H3+ is studied using high-sensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak ro-vibrational transitions from the lowest rotational states of H3+ up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein $B$ coefficients. {\it Ab initio} predictions for the Einstein $B$ coefficients are obtained from a highly precise dipole moment surface of H3+ and found to be in excellent agreement, even in the region where states have been classified as chaotic.

physics.chem-ph↗