Journal of Chemical Physics最新文献

Double excitations are crucial to understanding numerous chemical, physical, and biological processes, but accurately predicting them remains a challenge. In this work, we explore the particle-particle random phase approximation (ppRPA) as an efficient and accurate approach for computing double excitation energies. We benchmark ppRPA using various exchange-correlation functionals for 21 molecular systems and two point defect systems. Our results show that ppRPA with functionals containing appropriate amounts of exact exchange provides accuracy comparable to high-level wave function methods such as CCSDT and CASPT2, with significantly reduced computational cost. Furthermore, we demonstrate the use of ppRPA starting from an excited (N - 2)-electron state calculated by ΔSCF for the first time, as well as its application to double excitations in bulk periodic systems. These findings suggest that ppRPA is a promising tool for the efficient calculation of double and partial double excitation energies in both molecular and bulk systems.

2D porous material supported ionic liquid membranes (SILMs) have demonstrated great potential for CO2 separation and purification, outperforming the original porous material. However, the working mechanism behind their enhanced CO2 selectivity remains unclear. In this study, we have conducted molecular dynamics simulation to investigate the CO2/N2 separation performance and the underlying mechanism of SILMs taking 2D rhombic N-graphdiyne (r-N-GDY) with intrinsic high thermal stability and porous structure covered with 1-butyl-3-methylimidazolium tetrafluoroborate as the representative SILM model. We found that the increase in the SILM thickness can decrease the permeance of CO2 and N2 but can effectively increase the CO2/N2 selectivity. The optimal SILM thickness is found to be 0.6 nm with the permeance reaching 5.7 × 105 GPU for CO2 and the selectivity being up to 25.8, which is 15 times higher than the 1.7 of bare r-N-GDY. This is because CO2 encounters a much lower transmembrane energy barrier than N2. At the molecular level, it is fascinating to observe a cation-gating mechanism, where IL cations play a determinative role in CO2 selectivity. More specifically, the IL cations normally bind at the pore site, like a closed gate for gas. When a CO2 molecule approaches the pore, the IL cation moves away; thus, the gate is opened for CO2 translocation. In contrast, N2 molecules are incapable of opening the cation gate. Such a cation-gating process guarantees the high selectivity of SILMs. This study offers insight into enhanced CO2 selectivity and provides theoretical guidance for designing nanocomposite membranes for gas or water treatment.

We model the Hartree-exchange-correlation potential of Kohn-Sham (KS) density-functional theory adopting a novel strategy inspired by the strictly correlated-electron limit and relying on the exact decomposition of the potential based on the exact factorization formalism. Starting with accurate density and conditional potential for a one-dimensional model of a stretched heteronuclear molecule, we provide a proof-of-principle example of an approximation that accurately reproduces the step of the exact KS potential without resorting to the KS orbitals, virtual or occupied. We also test our strategy using the approximate conditional potentials corresponding to the strictly correlated-electron and the exact-exchange functionals. The results are encouraging in that the initial approximations are modified in the qualitatively correct way: decreasing correlation in the former and increasing it in the latter.

The water/electrode interface under an applied bias potential is a challenging out-of-equilibrium phenomenon, which is difficult to accurately model at the atomic scale. In this study, we employ a combined approach of density functional theory and non-equilibrium Green's function methods to analyze the influence of an external bias on the properties of water adsorbed on Au(111) and Pd(111) metallic electrodes. Our results demonstrate that while both Au and Pd-electrodes induce qualitatively similar structural responses in adsorbed water molecules, the quantitative differences are substantial, driven by the distinct nature of water-metal bonding. Our findings underscore the necessity of quantum-mechanical modeling for accurately describing electrochemical interfaces.

The behavior of silver nitrate in non-aqueous liquid oligomeric media-aromatic and aliphatic diglycidyl ethers and aliphatic diamine-has been investigated. By employing UV-visible spectrophotometry and dynamic light scattering, it has been shown that in diglycidyl oligomers, regardless of the nature of the monomeric unit, the formation of silver nanoparticles occurs, and the kinetics of this process has been studied. At the same time, in the medium of aliphatic diamine, the reduction of silver ions is absent, indicating the formation of a complex compound. XANES and EXAFS confirmed the formation of such a complex, established the probable coordination number of silver equal to three, and characterized the nearest atomic environment of silver. The SAXS results indicate the formation of complexes of extended conformation environment associated oligodiamine molecules, which favors the formation of an extended network of associates. The SAXS data were used to calculate the composition of the mixture of complexes and associates of diamine molecules for a saturated solution of silver nitrate in diamine. The results of this work will be used to develop new oligomer-silver nanocomposites with unique optical and bactericidal properties.

The exact quantum dynamics of lattice models can be computationally intensive, especially when aiming for large system sizes and extended simulation times necessary to converge transport coefficients. By leveraging finite memory times to access long-time dynamics using only short-time data, generalized master equations can offer a route to simulating the dynamics of lattice problems efficiently. However, such simulations are limited to small lattices whose dynamics exhibit finite-size artifacts that contaminate transport coefficient predictions. To address this problem, we introduce a novel approach that exploits finite memory in both time and space to efficiently predict the many-body dynamics of dissipative lattice problems involving short-range interactions. This advance enables one to leverage the short-time dynamics of small lattices to nonperturbatively and exactly simulate arbitrarily large systems over long times. We demonstrate the strengths of this method by focusing on nonequilibrium polaron relaxation and transport in the dispersive Holstein model, successfully simulating lattice dynamics in one and two dimensions free from finite-size effects, thereby reducing the computational expense of such simulations by multiple orders of magnitude. Our method is broadly applicable and provides an accurate and efficient means to investigate nonequilibrium relaxation with microscopic resolution over mesoscopic length and time scales that are relevant to experiments.

We introduce an approach to describe fractional charging of molecules interacting non-covalently with their environment. The formalism is based on dividing the full orbital space into orbitals localized to the molecule and orbitals localized to the environment. This enables a separation of the full electronic Hamiltonian into terms referencing only molecule, environment, or interaction terms. The interaction terms are divided into particle-conserving interactions and particle-non-conserving (particle-breaking) interactions. The particle-conserving interactions are dominant and may be included using standard embedding schemes. The particle-breaking terms are responsible for inducing fractional charging, and we show that the local orbital space approach provides a convenient framework for different types of perturbative treatments. In the local orbital basis, we generate a basis of many-electron states for the composite system, in which a specific molecular charge may label each state. This basis is used to construct a projection operator acting on the Liouville-von Neumann equation for the composite system to yield an equation for the reduced density matrix for the molecule. The diagonal elements of the reduced density matrix represent populations of different molecular charge states and determine the fractional charging. The projected Liouville-von Neumann equation is the starting point for two perturbative treatments: damped response theory and Redfield theory. The damped response framework introduces energy broadening of electronic states. Phenomenological broadening is also introduced into the Redfield equation. We illustrate the presented formalism by considering benzene physisorbed on a finite graphene sheet as a toy model.

In this study, we investigate the reliability of cluster perturbation (CP) theory applied to the calculation of electronically excited states through a comprehensive benchmark. In CP theory, perturbative corrections are added to the properties of a parent excitation space, which converge toward the properties of a target excitation space. For the CPS(D-n) model, perturbative corrections through order n are added to the coupled cluster singles (CCS) excitation energies to target the coupled cluster singles and doubles (CCSD) excitation energies. Through a comparative analysis of excitation energy calculations across a diverse set of molecules and wavefunction methods, we present a comprehensive evaluation of the accuracy of the third-order CPS(D) model, CPS(D-3), in calculating excitation energies. Our findings demonstrate that CPS(D-3) is a reliable alternative to established methods, particularly CCSD, while systematically overestimating the excitation energies compared to high-level coupled cluster methods such as CC3. These results highlight the strengths and limitations of CPS(D-3), as well as the promising directions for its future development.

We investigate with numerical simulations the influence of topology and stiffness on macroscopic rheological properties of polymer melts consisting of unknotted, knotted, or concatenated rings. While melts of flexible, knotted oligomer rings tend to be significantly more viscous than their unknotted counterparts, differences vanish in a low shear rate scenario with increasing degree of polymerization. Melts of catenanes consisting of two rings on the other hand are consistently more viscous than their unconcatenated counterparts. These topology-based differences in rheological properties can be exploited to segregate mixtures of otherwise chemically similar polymers, e.g., in microfluidic devices, which is demonstrated by exposing a blend of flexible knotted and unknotted oligomer rings to channel flow.

Close coupling calculations of line shape parameters have been performed for the first pure rotational R0(j = 0-4) lines of CO in helium baths at various temperatures. Besides the usual Lorentzian widths and shifts, we provide the complex Dicke parameters as well as the double power law temperature representation of all four parameters. In addition, we study the speed dependence of these parameters. The R0(0) and R0(1) theoretical thermally averaged collisional widths and shifts between 500 and about 15 K are in excellent agreement with the values reported in the literature. Below this temperature range, we confirm the persistent substantial disagreement that exists since 1985 between experimental and theoretical values. We thus focus on this regime, which is important for astrophysical applications, and we discuss various beyond-Voigt effects at low temperatures to try to understand this mismatch. We show that such mechanisms do not allow experimental widths and shifts to be reconciled with those from theory.