Materials in metastable states, such as amorphous ice and supercooled condensed matter, often exhibit exotic phenomena. To date, achieving metastability is usually accomplished by rapid quenching ...through a thermodynamic path function, namely, heating−cooling cycles. However, heat can be detrimental to organic-containing materials because it can induce degradation. Alternatively, the application of pressure can be used to achieve metastable states that are inaccessible via heating−cooling cycles. Here we report metastable states of 2D organic−inorganic hybrid perovskites reached through structural amorphization under compression followed by recrystallization via decompression. Remarkably, such pressure-derived metastable states in 2D hybrid perovskites exhibit enduring bandgap narrowing by as much as 8.2% with stability under ambient conditions. The achieved metastable states in 2D hybrid perovskites via compression−decompression cycles offer an alternative pathway toward manipulating the properties of these “soft” materials.
Electronic resonances are metastable states with finite lifetime embedded in the ionization or detachment continuum. They are ubiquitous in chemistry, physics, and biology. Resonances play a central ...role in processes as diverse as DNA radiolysis, plasmonic catalysis, and attosecond spectroscopy. This review describes novel equation-of-motion coupled-cluster (EOM-CC) methods designed to treat resonances and bound states on an equal footing. Built on complex-variable techniques such as complex scaling and complex absorbing potentials that allow resonances to be associated with a single eigenstate of the molecular Hamiltonian rather than several continuum eigenstates, these methods extend electronic-structure tools developed for bound states to electronic resonances. Selected examples emphasize the formal advantages as well as the numerical accuracy of EOM-CC in the treatment of electronic resonances. Connections to experimental observables such as spectra and cross sections, as well as practical aspects of implementing complex-valued approaches, are also discussed.
Exact milestoning Bello-Rivas, Juan M; Elber, Ron
The Journal of chemical physics,
03/2015, Volume:
142, Issue:
9
Journal Article
Peer reviewed
Open access
A new theory and an exact computer algorithm for calculating kinetics and thermodynamic properties of a particle system are described. The algorithm avoids trapping in metastable states, which are ...typical challenges for Molecular Dynamics (MD) simulations on rough energy landscapes. It is based on the division of the full space into Voronoi cells. Prior knowledge or coarse sampling of space points provides the centers of the Voronoi cells. Short time trajectories are computed between the boundaries of the cells that we call milestones and are used to determine fluxes at the milestones. The flux function, an essential component of the new theory, provides a complete description of the statistical mechanics of the system at the resolution of the milestones. We illustrate the accuracy and efficiency of the exact Milestoning approach by comparing numerical results obtained on a model system using exact Milestoning with the results of long trajectories and with a solution of the corresponding Fokker-Planck equation. The theory uses an equation that resembles the approximate Milestoning method that was introduced in 2004 A. K. Faradjian and R. Elber, J. Chem. Phys. 120(23), 10880-10889 (2004). However, the current formulation is exact and is still significantly more efficient than straightforward MD simulations on the system studied.
A production-level implementation of equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) for electron attachment and excitation energies augmented by a complex absorbing potential (CAP) ...is presented. The new method enables the treatment of metastable states within the EOM-CC formalism in a similar manner as bound states. The numeric performance of the method and the sensitivity of resonance positions and lifetimes to the CAP parameters and the choice of one-electron basis set are investigated. A protocol for studying molecular shape resonances based on the use of standard basis sets and a universal criterion for choosing the CAP parameters are presented. Our results for a variety of π(*) shape resonances of small to medium-size molecules demonstrate that CAP-augmented EOM-CCSD is competitive relative to other theoretical approaches for the treatment of resonances and is often able to reproduce experimental results.
Updated analyses of several singlet Rydberg states of O
2
via spectra involving excitation from the metastable a
1
Δ
g
and
states are presented. The high-quality FT-VUV spectra available from the ...DESIRS beamline at the SOLEIL synchrotron gives significantly improved spectra compared to previous work. The Rydberg states analysed include
v = 0-4, 3pσ
1
Π
u
v = 0-2, 3pπ
1
Δ
u
v = 0-2,
v = 0-1, 4pσ
1
Π
u
v = 0 and 4pπ
1
Δ
u
v = 0. This is complemented by high-quality ab initio calculations on the
and
1
Δ
u
Rydberg states to determine the transition moments providing the first quantitative cross-sections for Rydberg -
transitions. These are validated against the experimental data. The results suggest the most promising candidate for determining
number density is likely to be the 1-0 band of the
transition at 131.3 nm.
•The study of new unknown details in nitrogen spectroscopy is an important part of chemistry background.•A new spin-forbidden quintet-triplet C’’5Πu → B3Πg transition is predicted.•Transition ...probabilities for an unknown C’’5Пu → B3Пg system of vibronic bands are calculated.•We provide SOC constants calculated by MRCI calculations which are in a good agreement with experiment.•The experimental set-up designed to detect the C’’ → b transition can also be used to observe the A′→ a emission.
A new spin-forbidden quintet-triplet C′′5Πu → B3Πg transition is predicted in the N2 molecule on the ground of MRCI calculations with account of spin-obit coupling (SOC) by perturbation theory. The mechanism of its probability borrowing is quite similar to the recently calculated spin-forbidden electric dipole A′5Σg+ → A3Σu+ transition in the emission spectrum of the N2 molecule. Neither of the two predicted emission systems have yet been observed in electric discharges but the calculated intensity provides a good chance for their detection. Both transitions, C′′–B and A′–A, borrow intensity from the First Positive System (B3Πg → A3Σu+) and from the Herman Infrared Band (C′′5Πu → A′5Σg+). The latter spin-allowed quintet-quintet transition provides strong depletion of the upper C′′ state; nevertheless, the energy pooling collisions of the triplet N2 molecule and atomic recombination produce a permanent pumping of the C′′5Πu states leaving a prominent emission with a detectable quantum yield. The proposed C′′ → B vibronic transitions have Einstein A coefficients in the order of 105–104s −1, showing a considerable number of strong vibronic bands. As a consequence, the radiative lifetimes of the highest spin sublevel of the C′′5Πu,1 irregular state are about 10−6 s.
A new spin-forbidden quintet-triplet C′′ 5 Π u → B 3 Π g transition is predicted in the N 2 molecule on the ground of MRCI calculations with account of spin-obit coupling (SOC) by perturbation ...theory. The mechanism of its probability borrowing is quite similar to the recently calculated spin-forbidden electric dipole A′ 5 Σ g + → A 3 Σ u + transition in the emission spectrum of the N 2 molecule. Neither of the two predicted emission systems have yet been observed in electric discharges but the calculated intensity provides a good chance for their detection. Both transitions, C′′–B and A′–A, borrow intensity from the First Positive System (B 3 Π g → A 3 Σ u + ) and from the Herman Infrared Band (C′′ 5 Π u → A′ 5 Σ g + ). The latter spin-allowed quintet-quintet transition provides strong depletion of the upper C′′ state; nevertheless, the energy pooling collisions of the triplet N 2 molecule and atomic recombination produce a permanent pumping of the C′′ 5 Π u states leaving a prominent emission with a detectable quantum yield. The proposed C′′ → B vibronic transitions have Einstein A coefficients in the order of 10 5 –10 4 s − 1 , showing a considerable number of strong vibronic bands. As a consequence, the radiative lifetimes of the highest spin sublevel of the C′′ 5 Π u,1 irregular state are about 10 −6 s.
Perhaps the most iconic feature of melting Arctic sea ice is the distinctive ponds that form on its surface. The geometrical patterns describing how melt water is distributed over the surface largely ...determine the solar reflectance and transmittance of the sea ice cover, which are key parameters in climate modeling and upper ocean ecology. In order to help develop a predictive theoretical approach to studying melting sea ice, and the resulting patterns of light and dark regions on its surface in particular, we look to the statistical mechanics of phase transitions and introduce a two-dimensional random field Ising model which accounts for only the most basic physics in the system. The ponds are identified as metastable states in the model, where the binary spin variable corresponds to the presence of melt water or ice on the sea ice surface. With the lattice spacing determined by snow topography data as the only measured parameter input into the model, energy minimization drives the system toward realistic pond configurations from an initially random state. The model captures the essential mechanism of pattern formation of Arctic melt ponds, with predictions that agree very closely with observed scaling of pond sizes and transition in pond fractal dimension.
Schmitt-Triggers (S/Ts) are often utilized to clean noisy analog signals at intermediate voltage values in digital circuits. However, they are vulnerable to metastability, which may cause the same ...undesired non-digital output behavior that was supposed to be removed in the first place. To enable an efficient characterization of static and dynamic metastability properties of S/Ts (e.g., the metastable voltages, the resolution time constants and the overall total resolution times), this work introduces multiple simulation approaches based on control theory, AC, DC and transient analyses. The accuracy and runtime of all methods are compared and discussed by applying them to an analytically describable idealized circuit model as well as three common circuit implementations. Altogether, this work represents a comprehensive resource for investigating the metastable behavior in S/Ts. Even more, the proposed methods are applicable beyond the S/T, enabling an efficient characterization of static and dynamic metastable behavior in general circuits as well.
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