Chemical Physics
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Showing new listings for Friday, 22 November 2024
- [1] arXiv:2411.13747 [pdf, html, other]
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Title: Interfacial Water Polarization: A Critical Force for Graphene-based Electrochemical InterfacesSubjects: Chemical Physics (physics.chem-ph)
Water molecules predominantly act as solvents in electrochemical systems and are often modeled as a passive dielectric medium. In this work, we use molecular dynamics simulations and theoretical analysis to revisit this conventional view. We reveal that the interfacial polarized water overscreens the electrostatic potential between ions and the surface beyond being a passive dielectric medium. This overscreening enables the interfacial water to dominate the electric potential spatial distribution, inverting the electrode surface potential polarity and dominating the capacitance. A model is then developed to incorporate this critical interfacial water polarization.
- [2] arXiv:2411.13866 [pdf, html, other]
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Title: A Phase-Space Electronic Hamiltonian for Molecules in a Static Magnetic Field I: Conservation of Total Pseudomomentum and Angular MomentumSubjects: Chemical Physics (physics.chem-ph)
We develop a phase-space electronic structure theory of molecules in magnetic fields. For a system of electrons in a magnetic field with vector potential $\bf{A}(\hat{\bf{r}})$, the usual Born-Oppenheimer Hamiltonian is the sum of the nuclear kinetic energy and the electronic Hamiltonian, $\frac{(\bf{P} - q\bf{A}(\bf{X}) )^2}{2M} + \hat{H}_{e}(\bf{X})$ (where $q$ is a nuclear charge). To include the effects of coupled nuclear-electron motion in the presence of magnetic field, we propose that the proper phase-space electronic structure Hamiltonian will be of the form $\frac{(\bf{P} - q^{\textit{eff}}\bf{A}(\bf{X}) - e\hat{\bf{\Gamma}})^2}{2M} + \hat{H}_{e}(\bf{X})$. Here, $q^{\textit{eff}}$ represents the {\em screened} nuclear charges and the $\hat{\bf{\Gamma}}$ term captures the local pseudomomentum of the electrons. This form reproduces exactly the energy levels for a hydrogen atom in a magnetic field; moreover, single-surface dynamics along the eigenstates is guaranteed to conserve both the total pseudomomentum as well as the total angular momentum in the direction of the magnetic field. This Hamiltonian form can be immediately implemented within modern electronic structure packages (where the electronic orbitals will now depend on nuclear position ($\bf{X}$) and nuclear momentum ($\bf{P}$)). One can expect to find novel beyond Born-Oppenheimer magnetic field effects for strong enough fields and/or nonadiabatic systems.
- [3] arXiv:2411.13879 [pdf, html, other]
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Title: A Phase-Space Electronic Hamiltonian for Molecules in a Static Magnetic Field II: Quantum Chemistry Calculations with Gauge Invariant Atomic OrbitalsSubjects: Chemical Physics (physics.chem-ph)
In a companion paper, we have developed a phase-space electronic structure theory of molecules in magnetic fields, whereby the electronic energy levels arise from diagonalizing a phase-space Hamiltonian $\hat H_{PS}(\bf{X},\bf{\Pi})$ that depends parametrically on nuclear position and momentum. The resulting eigenvalues are translationally invariant; moreover, if the magnetic field is in the $z-$direction, then the eigenvalues are also invariant to rotations around the $z-$direction. However, like all Hamiltonians in a magnetic field, the theory has a gauge degree of freedom (corresponding to the position of the magnetic origin in the vector potential), and requires either $(i)$ formally, a complete set of electronic states or $(ii)$ in practice, gauge invariant atomic orbitals (GIAOs) in order to realize such translational and rotational invariance. Here we describe how to implement a phase-space electronic Hamiltonian using GIAOs within a practical electronic structure package (in our case, Q-Chem). We further show that novel phenomena can be observed with finite $\bf{B}-$fields, including minimum energy structures with $\bf{\Pi}_{min} \ne 0$, indicating non-zero electronic motion in the ground-state.
- [4] arXiv:2411.13986 [pdf, html, other]
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Title: On the applicability of CCSD(T) for dispersion interactions in large conjugated systemsSubjects: Chemical Physics (physics.chem-ph)
In light of the recent discrepancies reported between fixed node diffusion Monte Carlo and local natural orbital coupled cluster with single, double and perturbative triples (CCSD(T)) methodologies for non-covalent interactions in large molecular systems [Al-Hamdani et al., Nat. Comm., 2021, 12, 3927], the applicability of CCSD(T) is assessed using a model framework. The use of the Pariser-Parr-Pople (PPP) model for studying large molecules is critically examined and is shown to recover both bandgap closure as system size increases and long range dispersive behavior of r^-6 with increasing separation between monomers, in corollary with real systems. Using the PPP model, coupled cluster methodologies, CCSDTQ and CCSDT(Q), are then used to benchmark CCSDT and CCSD(T) methodologies for non-covalent interactions in large one- and two-dimensional molecular systems up to the dibenzocoronene dimer. We show that CCSD(T) demonstrates no signs of overestimating the interaction energy for these systems. Furthermore, by examining the Hartree-Fock HOMO-LUMO gap of these large molecules, the perturbative treatment of the triples contribution in CCSD(T) is not expected to cause problems for accurately capturing the interaction energy for system sizes up to at least circumcoronene.
- [5] arXiv:2411.14134 [pdf, html, other]
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Title: Simulating Nonadiabatic Dynamics in Benzophenone: Tracing Internal Conversion Through Photoelectron SpectraSubjects: Chemical Physics (physics.chem-ph)
Benzophenone serves as a prototype chromophore for studying the photochemistry of aromatic ketones, with applications ranging from biochemistry to organic light-emitting diodes. In particular, its intersystem crossing from the first singlet excited state to triplet states has been extensively studied, but experimental or theoretical studies on the preceding internal conversion within the singlet manifold are very rare. This relaxation mechanism is particularly important because direct population transfer of the first singlet excited state from the ground state is inefficient due to its low oscillator strength. In this work, we aim to fill this gap by employing mixed quantum classical and full quantum dynamics simulations and time-resolved photoelectron spectroscopy for gas-phase benzophenone and meta-methyl benzophenone. Our results show that nonadiabatic relaxation via conical intersections leads to a linear increase in the population of the first singlet excited state. This population transfer due to conical intersections can be directly detected by a bifurcation of the photoelectron signal. In addition, we are able to clarify the role of the third singlet excited state degenerate to the second excited state - a topic that remains largely unexplored in the existing literature on benzophenone.
- [6] arXiv:2411.14282 [pdf, html, other]
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Title: Singlet Fission in Carotenoid Dimers -- The Role of the Exchange and Dipolar InteractionsSubjects: Chemical Physics (physics.chem-ph)
A theory of singlet fission in carotenoid dimers is presented which aims to explain the mechanism behind the creation of two uncorrelated triplets. Following the initial photoexcitation of a carotenoid chain to a "bright" $n^1B_u^+$ state, there is ultrafast internal conversion to the intrachain "dark" $1^1B_u^-$ triplet-pair state. This strongly exchanged-coupled state evolves into a pair of triplets on separate chains and spin-decoheres to form a pair of single, unentangled triplets, corresponding to complete singlet fission. The simulated EPR spectra for lycopene dimers shows a distinct spectral signal due to the residual exchange coupling between the triplet-pairs on seperate carotenoid chains.
New submissions (showing 6 of 6 entries)
- [7] arXiv:2411.14061 (cross-list from cond-mat.mtrl-sci) [pdf, other]
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Title: One-step Synthesis of Cubic Gauche Polymeric Nitrogen with High Yield Just by HeatingComments: 7 pages, 4 figuresSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
A high-efficient one-step synthesis of cubic gauche polymeric nitrogen was developed just by thermal treatment of KN3 powders. The Raman and infrared spectra confirm the formation of polymeric nitrogen networks. Thermogravimetric differential scanning calorimeter measurements show that the content of cubic gauche polymeric nitrogen is as high as 1.5 wt% with high thermal stability, which is the highest content value so far.
- [8] arXiv:2411.14289 (cross-list from cond-mat.mtrl-sci) [pdf, html, other]
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Title: Octahedral tilt-driven phase transitions in BaZrS3 chalcogenide perovskiteSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
Chalcogenide perovskites are lead-free materials for potential photovoltaic or thermoelectric applications. BaZrS$_3$ is the most studied member of this family due to its superior thermal and chemical stability, desirable optoelectronic properties, and low thermal conductivity. Phase transitions of the BaZrS$_3$ perovskite are under-explored in literature as most experimental characterization is performed at ambient conditions where the orthorhombic Pnma phase is reported to be stable. In this work, we study the dynamics of BaZrS$_3$ across a range of temperatures and pressures using an accurate machine-learned interatomic potential trained with data from hybrid density functional theory calculations. At 0Pa, we find a first-order phase transition from the orthorhombic to tetragonal I4/mcm phase at 610K, and a second-order transition from the tetragonal to the cubic Pm-3m phase at 880K. The tetragonal phase is stable over a larger temperature range at higher pressures. To confirm the validity of our model we report the static structure factor as a function of temperature and compare our results with published experimental data.
Cross submissions (showing 2 of 2 entries)
- [9] arXiv:2409.19249 (replaced) [pdf, html, other]
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Title: Enhancing the ODMR Signal of Organic Molecular QubitsComments: 11 pages, 5 figures. Some rephrasing was done for better readability and the figure texts have been enlargedSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
In quantum information science and sensing, electron spins are often purified into a specific polarisation through an optical-spin interface, a process known as optically-detected magnetic resonance (ODMR). Diamond-NV centres and transition metals are both excellent platforms for these so-called colour centres, while metal-free molecular analogues are also gaining popularity for their extended polarisation lifetimes, milder environmental impacts, and reduced costs. In our earlier attempt at designing such organic high-spin $\pi$-diradicals, we proposed to spin-polarise by shelving triplet $M_{S}=\pm1$ populations as singlets. This was recently verified by experiments albeit with low ODMR contrasts of $<1\%$ at temperatures above 5 K. In this work, we propose to improve the ODMR signal by moving singlet populations back into the triplet $M_{S}=0$ sublevel, designing a true carbon-based molecular analogue to the NV centre. Our proposal is based upon transition-orbital and group-theoretical analyses of beyond-nearest-neighbour spin-orbit couplings, which are further confirmed by ab initio calculations of a realistic trityl-based radical dimer. Microkinetic analyses point towards high ODMR contrasts of around $30\%$ under experimentally-feasible conditions, a stark improvement from previous works. Finally, in our quest towards ground-state optically-addressable molecular spin qubits, we exemplify how our symmetry-based design avoids Zeeman-induced singlet-triplet mixings, setting the scene for realising electron spin qubit gates.
- [10] arXiv:2410.15159 (replaced) [pdf, other]
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Title: Cryogenic W-band Electron Spin Resonance Probehead with an Integral Cryogenic Low Noise AmplifierComments: 29 pages, 11 figuresSubjects: Chemical Physics (physics.chem-ph)
The quest to enhance the sensitivity of electron spin resonance (ESR) is an ongoing challenge. One potential strategy involves increasing the frequency, for instance, moving from Q-band (approximately 35 GHz) to W-band (approximately 94 GHz). However, this shift typically results in higher transmission and switching losses, as well as increased noise in signal amplifiers. In this work, we address these shortcomings by employing a W-band probehead integrated with a cryogenic low-noise amplifier (LNA) and a microresonator. This configuration allows us to position the LNA close to the resonator, thereby amplifying the acquired ESR signal with minimal losses. Furthermore, when operated at cryogenic temperatures, the LNA exhibits unparalleled noise levels that are significantly lower than those of conventional room temperature LNAs. We detail the novel probehead design and provide some experimental results at room temperature as well as cryogenic temperatures for representative paramagnetic samples. We find, for example, that spin sensitivity of ~3*10^5 spins/sqrt(Hz) is achieved for a sample of phosphorus doped 28Si, even for sub-optimal sample geometry with potential improvement to <10^3 spins/sqrt(Hz) in more optimal scenarios.
- [11] arXiv:2301.05666 (replaced) [pdf, html, other]
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Title: Beyond MP2 initialization for unitary coupled cluster quantum circuitsSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
The unitary coupled cluster (UCC) ansatz is a promising tool for achieving high-precision results using the variational quantum eigensolver (VQE) algorithm in the NISQ era. However, results on quantum hardware are thus far very limited and simulations have only accessed small system sizes. We advance the state of the art of UCC simulations by utilizing an efficient sparse wavefunction circuit solver and studying systems up to 64 qubits. Here we report results obtained using this solver that demonstrate the power of the UCC ansatz and address pressing questions about optimal initial parameterizations and circuit construction, among others. Our approach enables meaningful benchmarking of the UCC ansatz, a crucial step in assessing the utility of VQE for achieving quantum advantage.
- [12] arXiv:2401.16374 (replaced) [pdf, html, other]
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Title: Analytic Model Reveals Local Molecular Polarizability Changes Induced by Collective Strong Coupling in Optical CavitiesSubjects: Quantum Physics (quant-ph); Chemical Physics (physics.chem-ph)
Despite recent numerical evidence, one of the fundamental theoretical mysteries of polaritonic chemistry is how and if collective strong coupling can induce local changes of the electronic structure to modify chemical properties. Here we present non-perturbative analytic results for a model system consisting of an ensemble of $N$ harmonic molecules under vibrational strong coupling (VSC) that alters our present understanding of this fundamental question. By applying the cavity Born-Oppenheimer partitioning on the Pauli-Fierz Hamiltonian in dipole approximation, the dressed many-molecule problem can be solved self-consistently and analytically in the dilute limit. We discover that the electronic molecular polarizabilities are modified even in the case of vanishingly small single-molecule couplings. Consequently, this non-perturbative local polarization mechanism persists even in the large-$N$ limit. In contrast, a perturbative calculation of the polarizabilities leads to a qualitatively erroneous scaling behavior with vanishing effects in the large-$N$ limit. Nevertheless, the exact (self-consistent) polarizabilities can be determined from single-molecule strong coupling simulations instead. Our fundamental theoretical observations demonstrate that hitherto existing collective-scaling arguments are insufficient for polaritonic chemistry and they pave the way for refined single- (or few-) molecule strong-coupling ab-initio simulations of chemical systems under collective strong coupling.
- [13] arXiv:2410.08887 (replaced) [pdf, html, other]
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Title: How Semilocal Are Semilocal Density Functional Approximations? -Tackling Self-Interaction Error in One-Electron SystemsSubjects: Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)
Self-interaction error (SIE), arising from the imperfect cancellation of the spurious classical Coulomb interaction between an electron and itself, is a persistent challenge in modern density functional approximations. This issue is illustrated using the prototypical one-electron system $H_2^+$. While significant efforts have been made to eliminate SIE through the development of computationally expensive nonlocal density functionals, it is equally important to explore whether SIE can be mitigated within the framework of more efficient semilocal density functionals. In this study, we present a non-empirical meta-generalized gradient approximation (meta-GGA) that incorporates the Laplacian of the electron density. Our results demonstrate that the meta-GGA significantly reduces SIE, yielding a binding energy curve for $H_2^+$ that matches the exact solution at equilibrium and improves across a broad range of bond lengths over those of the Perdew-Burke-Ernzerhof (PBE) and strongly-constrained and appropriately-normed (SCAN) semilocal density functionals. This advancement paves the way for further development within the realm of semilocal approximations.