The Journal of Chemical Physics

The low-frequency vibrational dynamics of water (i.e., 0-1000cm-1) encodes rich details about its local environment, hydrogen bonding, and collective motion that are essential to water's various unique properties that are incredibly important for life in a manner that is easily comparable between experiments and simulations. This study uses molecular dynamics to perform a comprehensive mode-resol…

We present a comprehensive computational study of unbiased translocation of uncharged, coarse-grained polymers of short and intermediate length through thin nanopores. Simulations combine Langevin dynamics with forward flux sampling to monitor translocation without external bias. The results demonstrate quasi-equilibrium behavior such that the process is well described by projection onto a single…

Polymer solutions adjacent to solid substrates play a fundamental role in a wide range of polymeric systems, such as colloidal suspensions and biomolecular condensates, yet the understanding of the surface phase behaviors of polymer solutions, particularly in poor solvents, remains far from complete. In this work, by using a grand-canonical self-consistent field theory, we systematically examine …

We explore the performance of the time-convolutionless (TCL) projection operator technique using the Fano-Anderson model as a test case. Comparing the exact TCL master equation with an expansion in powers of the strength of the system-environment coupling, we analyze the transient dynamics as well as the steady-state behavior. For a Lorentzian spectral density, we demonstrate that the dimensionle…

We report on an experimental investigation of the photoabsorption of cold (∼30 K) C6- anions in the range 420-650 nm by laser two-photon photodetachment on a stored beam of anions in a merged beams interaction setup. The recorded photoabsorption spectrum shows evidence for photoabsorption through the lowest 2Πg states (labeled C, D, and E) with new assignments of the term values of T0.C = 1.9363 …

Porous ice represents an emerging class of crystalline ice phases characterized by extensive nano-cavities and/or nano-channels within their hydrogen-bonded water frameworks. The prediction of ultralow-density porous ices is of particular interest, as their high surface-to-volume ratio could significantly expand their practical applications. In this work, we assembled two series of ultralow-densi…

Ultra-small-angle neutron scattering (USANS) using Bonse-Hart optics provides micrometer-scale structural insights but suffers from severe slit-geometry smearing. While well-established for isotropic systems, quantitative desmearing of anisotropic data remains a challenge because conventional corrections break down for non-radial scattering. We address this by developing a resolution-aware Bayesi…

Theoretical models of paramagnetic relaxation enhancement effects have been tested for 1H spin-lattice relaxation in water solutions of core-shell nanoparticles composed of NaDyF4 (core) and NaGdF4 (shell). The experimental data used for this testing have been collected in a broad frequency range, from 10 kHz to 400 MHz, vs temperature, for the core radius of the nanoparticles of 11 nm and the sh…

We extend existing phase-field simulation methods to develop an accurate method for simulating ice growth in aqueous solutions. This method is then applied to model ice growth in sucrose-water solutions. Starting with a model for the free energy of the sucrose solution in coexistence with ice, we describe its equilibrium thermodynamics. This results in a phase diagram for solutions of sucrose in …

Water cluster cations serve as prototypical models for ionized aqueous environments and provide an ideal platform for examining the stability of O-O hemi-bonded motifs. Despite extensive studies, the relative energetics of hemi-bonded and proton-transferred structures, as well as their dissociation behavior, remain challenging to describe accurately. In this work, we present a systematic benchmar…

Machine learning interatomic potentials (MLIPs) balance high accuracy and lower costs compared to density functional theory calculations, but their performance often depends on the size and diversity of training datasets. Large datasets improve model accuracy and generalization but are computationally expensive to produce and train on, while smaller datasets risk discarding rare but important ato…

We study a segmentally active Rouse chain in which activity is confined to a single contiguous segment of tunable length and position along the contour. Employing analytical normal-mode theory together with Brownian-dynamics simulations, we quantify how localized activity governs conformation and dynamics. Using global conformational measures such as the mean square radius of gyration and end-to-…

The vibrational energy relaxation dynamics of the excited free OH bond on the ice surface are investigated using ab initio molecular dynamics (AIMD) simulations. The present AIMD study reproduces experimental results obtained via pump-probe sum-frequency generation spectroscopy. Simulations were conducted at 100 and 200 K for ice surfaces and compared with previous results at 300 K for water surf…

Instanton theory has arisen as a practical tool for calculating tunneling splittings in molecular systems. Unfortunately, the original formulation of instanton theory fundamentally breaks down when trying to calculate the level splitting in asymmetric double wells, as there is no imaginary-time periodic orbit connecting the two non-degenerate minima. We have, therefore, developed a new formulatio…

Ab initio quantum Monte Carlo (QMC) methods are state-of-the-art electronic structure calculations based on highly parallelizable stochastic frameworks for accurate solutions of the many-body Schrödinger equation, suitable for modern many-core supercomputer architectures. Despite its potential, one of the major drawbacks that still hinders QMC applications, especially when targeting dynamical pro…

Electrochemical applications, ranging from energy storage to electrocatalysis and separations, involve ions in heterogeneous environments such as electrode/electrolyte interfaces, material interphases, and confined spaces. These environments influence ion thermodynamics through their effect on chemical potentials and, consequently, on the driving forces relevant to ion transport and electrochemic…

We present new and computationally efficient implementation of the equation-of-motion (EOM) coupled-cluster methods for doubly ionized (DIP) and doubly electron-attached (DEA) states including single, double, and triple substitutions. In particular, EOM operators include up to 4-hole-2-particle substitutions in EOM-DIP-CCSDT and up to 4-particle-2-holes substitutions in EOM-DEA-CCSDT; both treatm…

In this study, we report an analytical derivative implementation of static polarizability gradients, needed for the prediction of Raman spectra, in the ORCA program. Our implementation is capable of handling density functionals up to the meta-GGA level and makes use of RIJ and COSX integral approximations to improve the scaling of calculations using both pure and hybrid functionals. Solvent effec…

The solvation shell around a solute is a fundamental feature of liquid-phase solutions, determining the behavior and properties of both the solute and the overall solution. Direct experimental measurements of the solvation shell properties are challenging due to the strong signals generated from the bulk solvent, which overwhelm the small contribution of the solvation shell. Here, we use ultrafas…

While sum frequency generation (SFG) spectroscopy is known to have acute interface selectivity owing to the dipole approximation, it has been a long-standing concern to understand the contribution of higher-order polarizations and/or bulk. Motivated by recent advances in microscopic theory of SFG including quadrupole, this work reports our recent development of the calculation tool of quadrupole …