Search

In this paper, we study the correspondence between the three-dimensional and one-dimensional physical quantity in the spherically symmetric gravitational fields and we obtain a conjecture that the total energy enclosed by the two-dimensional sphere is equal to twice the change in vacuum zero-point energy of a one-dimensional circle that is the boundary of a hemispherical sphere, we can naturally obtain Schwarzschild metric without relying on Einstein's gravitational field equation under this conjecture, the result leads us to conclude that gravity originates from the change of zero-point energy in the one-dimensional vacuum.

We give a vacuum description with zero-point density for virtual fluctuations. One of the goals is to explain the origin of the vacuum permittivity and permeability and to calculate their values. In particular, we improve on existing calculations by avoiding assumptions on the volume occupied by virtual fluctuations. We propose testing of the models that assume a finite lifetime of virtual fluctuation. If during its propagation, the photon is stochastically trapped and released by virtual pairs, the propagation velocity may fluctuate. The propagation time fluctuation is estimated for several existing models. The obtained values are measurable with available technologies involving ultra-short laser pulses, and some of the models are already in conflict with the existing astronomical observations. The phase velocity is not affected significantly, which is consistent with the interferometric measurements.

Fourier-transform microwave spectroscopy has been applied for the 13C/18O-substituted tropolone to observe tunneling-rotation transitions as well as pure rotational transitions. The tunneling-rotation transitions were observed between the 13C-4 and -6 forms as well as between 13C-3 and -7, between 13C-1 and -2, and between 18O-8 and -9 (we denote these tunneling pairs as 13C-46, etc., below) although they have an asymmetric tunneling potential due to the difference in the zero point energy (ZPE). From the observed tunneling splittings ΔEij (0.9800–1.6824 cm−1), the differences in ZPE Δij for the 13C-46, -37, -12, and 18O-89 species are derived to be −0.1104, 0.5652, −1.3682, and 1.3897 cm−1 to agree well with the DFT calculation. The state mixing ratio of the tunneling states decreases drastically from (44%:56%) to (8.7%:91.3%) for 13C-46 and 18O-89 with an increase in the asymmetry Δij of the tunneling potential function. The observed tunneling-rotation interaction constants Fij decrease from 16.001 to 9.224 cm−1 as the differences in ZPE Δij increase, while the diagonal tunneling-rotation interaction constants Fu increase from 1.767 to 13.70 cm−1, explained well by the mixing ratio of the tunneling states. [ABSTRACT FROM AUTHOR]

To study the effect of hydrogen isotope substitution on the uptake of water during formation of clathrate hydrates, the harmonic intermolecular librational modes of selected water clusters (X2O)n with n = 2–6 and hydrogen isotopes X = H, D, and T are studied. The effects of the quantum mechanical zero-point energy (ZPE) in each cluster on the binding energies of the H2O, D2O, and T2O clusters are determined, with ZPE leading to the smallest binding energies in the H2O clusters and the largest binding energies in the T2O clusters. Corrections for anharmonicity of the librational modes are considered, and these bring the frequency ranges of the calculated intermolecular librational modes in the clusters to the experimental ranges of the librational modes in the infrared spectra of H2O and D2O solid ice and clathrate hydrate phases, and liquid H2O water. These calculations show the expected ranges of the binding energy of tritiated water onto a solid ice and clathrate hydrate surface and can help quantify the isotopic enrichment on a growing clathrate hydrate phase from the solution.

We present the first observation of vibrational transitions in the [H 3 O] - anion, an intermediate in the anion-molecule reaction of water, H 2 O, and hydride, H - , using a laser-induced isotopic H/D exchange reaction action spectroscopy scheme applied to anions. The observed bands are assigned as the fundamental and first overtone of the H 2 O-H - vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the D 2 O·D - species has the lowest energy, our experiments confirm the D 2 O·H - isotope to be a sink of the H/D exchange reaction. Ab initio calculations corroborate that the formation of D 2 O·H - is favored, as the zero-point-energy difference is larger between D 2 and H 2 than between D 2 O·H - and D 2 O·D - .

In this work, we characterize the temperature dependence of kinetic properties in heavy atom tunneling reactions by means of molecular dynamics simulations, including nuclear quantum effects (NQEs) via Path Integral theory. To this end, we consider the prototypical Cope rearrangement of semibullvalene. The reaction was studied in the 25–300 K temperature range observing that the inclusion of NQEs modifies the temperature behavior of both free energy barriers and dynamical recrossing factors with respect to classical dynamics. Notably, while in classical simulations the activation free energy shows a very weak temperature dependence, it becomes strongly dependent on temperature when NQEs are included. This temperature behavior shows a transition from a regime where the quantum effects are limited and can mainly be traced back to zero point energy, to a low temperature regime where tunneling plays a dominant role. In this regime, the free energy curve tunnels below the potential energy barrier along the reaction coordinate, allowing much faster reaction rates. Finally, the temperature dependence of the rate constants obtained from molecular dynamics simulations was compared with available experimental data and with semi‐classical transition state theory calculations, showing comparable behaviors and similar transition temperatures from thermal to (deep) tunneling regime. [ABSTRACT FROM AUTHOR]

To study the effect of hydrogen isotope substitution on the uptake of water during formation of clathrate hydrates, the harmonic intermolecular librational modes of selected water clusters (X2O)n with n = 2–6 and hydrogen isotopes X = H, D, and T are studied. The effects of the quantum mechanical zero-point energy (ZPE) in each cluster on the binding energies of the H2O, D2O, and T2O clusters are determined, with ZPE leading to the smallest binding energies in the H2O clusters and the largest binding energies in the T2O clusters. Corrections for anharmonicity of the librational modes are considered, and these bring the frequency ranges of the calculated intermolecular librational modes in the clusters to the experimental ranges of the librational modes in the infrared spectra of H2O and D2O solid ice and clathrate hydrate phases, and liquid H2O water. These calculations show the expected ranges of the binding energy of tritiated water onto a solid ice and clathrate hydrate surface and can help quantify the isotopic enrichment on a growing clathrate hydrate phase from the solution. [ABSTRACT FROM AUTHOR]

A model of an extended manifold for the Dirac spinor field is considered. Two Lagrangians related by charge-parity-time-mass symmetry are constructed for a pair of the Dirac spinor fields with each spinor field defined in a separate manifold. An interaction between the matter fields in the manifolds is introduced through gravity. A fermionic effective action of the general system is constructed and a tadpole one-loop spinor diagram and part of the one-loop vacuum diagrams with two external gravitational off-shell fields which contribute to the effective action are calculated. It is demonstrated that among different versions of the second spinor Lagrangian there is a special one for which a cancellation of the mentioned diagrams in the total effective action takes place. As a result, the diagrams do not contribute to the cosmological constant, as well there is a zero contribution of the zero point energies of the spinor fields to the action. The non-zero leading order value of the cosmological constant for each manifold in the framework is proportional to the trace of an momentum–energy tensor of each separated manifold or difference of the tensors of the related manifolds. The result is depending on the chosen model of interaction of gravitational fields with fermions, the different possibilities are discussed. An appearance of the dark matter in the model is shortly discussed as well as further applications of the approach and it is interconnections with other cosmology models. [ABSTRACT FROM AUTHOR]

An ab-initio investigation has been conducted for exploring the vibrational properties of very small size ZnxTey (x + y = 2 to 5 atoms) nanoclusters, which are obtained by density functional theory method (B3LYP-DFT/LANL2DZ). We have predicted here the vibrational frequencies, Infrared intensities (IR), Relative Infrared intensities and Raman scattering activities of the most stable ZnxTey (x + y = 2 to 5 atoms) nanoclusters. The structure having minimum energy in comparison to other structures having same values of "x" and "y" is considered as most stable. The zero point energy correction is also considered. ZnTe4 nanoclusters do not show any stable structure as all their configurations have at least one or more imaginary vibrational frequencies leading to their instability. The vibrational frequencies having higher values of each most stable nanocluster corresponds to the asymmetrical and symmetrical stretching vibrations whereas the frequencies having lower values corresponds to rocking, breathing, wagging and the out of plane vibrations of Zn and Te atoms of their corresponding nanocluster. [ABSTRACT FROM AUTHOR]

The COVID-19 is recognized as one of the deadly disease in the history of human life. It is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since its first case appeared in December 2019 in Wuhan, China, number of COVID-19 cases are still growing worldwide, till now number of confirmed COVID-19 cases reported globally are 594 million and number of fatalities are 6.29 million. It creates panic situation on every individual as well as put an extraordinary challenge on every country, especially on the health care system. The ruthlessness of the disease and its noxious complexities need development of suitable and effective drug on urgent basis to prevent as well as treat COVID-19. Though specific drug with proper efficacy is not yet found, a number of research and clinical trials are still going on to check the suitability and effectiveness of existing drug, i.e. repurposed drug to treat patients of COVID-19. In this article, repurposed drug—arbidol, baricitinib, favipiravir, galidesivir and ribavirin are reported by using Conceptual Density Functional Theory (CDFT) approach. Optimization energy, spin multiplicity, zero point energy correction, CDFT-based descriptors, optical and thermochemical properties of these repurposed drugs are computed and analysed. Result signify that favipiravir is the most reactive compound whereas ribavirin is found as the most stable among these molecular species. Favipiravir has the lowest thermal energy, heat capacity and entropy, whereas arbidol has the maximum thermal energy, heat capacity and entropy. There is an interesting correlation found between optimization energy, zero point energy correction, polarizability and thermochemical properties of these repurposed drugs. [ABSTRACT FROM AUTHOR]

The stability of trapped bosons with repulsive interaction is studied using an approximate many-body calculation. Instead of using the traditional harmonic trapping potential we consider an anharmonic potential of the form V anhar (r) = 1 2 m ω 2 r 2 + λ r 4 . In our method, a correlated two-body basis function is used which considers all two-body correlations. It is explained that negative value of anharmonic parameter (λ ) are capable to change a stable condensate into a metastable one. Within this metastable condensate, we slowly increase the number of atom (A) and find a collapsing nature of repulsive condensate. The process of collapse of repulsive Bose–Einstein condensation (BEC) is completely different from the collapsing process of attractive BEC and it is explained in details. A dramatic behaviour of interaction energy, kinetic energy, trapping potential energy along with the total ground state energy of this metastable repulsive BEC is observed. We also study the instability of these zero point energies by varying λ when fixed number of bosons are trapped by the anharmonic well and find critical values of λ at which the system collapses. When the number of trapped particle is sufficiently high, a close interplay between number of particle and anharmonic strength is observed to remodel the shape of the effective metastable region. [ABSTRACT FROM AUTHOR]

Each of the exchange–correlation functionals in the density functional theory has been customized to particular systems or elements and has unique advantages and disadvantages. In one of the most recent research on exchange–correlation functionals, Chachiyo et al. present a relationship for exchange–correlation functional by assuming the simplest form of electron density. Their utilized electron density causes a systematic inaccuracy in the energy of the molecules since it does not fully account for the variation of the ionization energy for different atoms. We offer a novel relationship for exchange functional that improves the precision of the energy calculations for molecules by using the basic assumptions of the Chachiyo approach and correcting the electron density. Our density is directly related to the atom's ionization energy. Our suggested functional was implemented for 56 molecules composed of atoms from the first, second, and third rows of the periodic table using Siam Quantum package. We discussed about the role of our functional on the reducing the computation error of dipole moment along with total, bonding and zero point energies. We also increased the portion of core electrons to improve the accuracy of the results. [ABSTRACT FROM AUTHOR]

It is postulated that the energy density of the (quantum) vacuum acts firstly as dark energy and secondly as a part of dark matter. Assisted by electric fields arising from a small charge mismatch in the cosmic plasma, it can condense on mass concentrations. No longer participating in the cosmic expansion, this constitutes “electro-aether-energy” (EAE), “electro-zero-point-energy” or “electro-vacuum-energy”, which solves the dark matter riddle without new physics. A radial electric field of 1 kV/m is predicted in the Galaxy. For proper electric fields, EAE can cover the results deduced with MOND. An instability allows a speedy filling of dark matter cores. Hydrostatic equilibrium in galaxy clusters is obeyed. Flowing in aether energy of explains why black holes become supermassive, do not have mass gaps and overcome the final parsec problem. Rupture of charged clouds reduces, e.g., the primordial baryon cloud to the cosmic web. The large coherence scale of the electric field acts as a scaffold for gentle galaxy formation and their vast polar structures. In galaxy merging and bars, there occurs no dynamical friction. At cosmological scales, EAE acts as pressureless dark matter. Its amount increases in time, which likely solves the Hubble tension by its late time physics. A big crunch can occur. Of the large cosmological constant injected at the Big Bang, a small part kept that form, without fine-tuning.

[Display omitted] • Thermal mid-IR emissions resonating with LO or LO-like phonons. • This emission is from the surface metal–semiconductor grating structures. • Spectrum peak energy depends on the LO-phonon and Reststrahlen band width. • Material-dependent emission efficiency is elucidated. • Balance of radiative and nonradiative LO-phonon annihilation dominates the efficiency. Infrared thermal radiation emission in the 8.5 – 28 THz frequency region is obtained using surface metal–semiconductor grating structures on undoped (u-) GaAs, u-GaP, u-ZnO, u-GaN, and n-type SiC in a temperature range of 430 – 630 K. These emissions resonate with longitudinal optical (LO) phonon or LO-like lattice vibration energies determined by the zero points of the real parts of the dielectric functions in the surface structures. The emissions of materials with Reststrahlen bandwidths of a few tens of cm−1 show the emissions resonating with their LO phonon modes, while materials with bandwidth of more than 170 cm−1 show peak energies significantly lower than the LO phonon: LO-like phonon resonance. The emission intensity is found to be dominated by the balance of radiative and nonradiative LO or LO-like phonon annihilation rates. The radiative rate is dominated by the LO-phonon–radiation interaction Hamiltonian and the Bose-Einstein factor. High emission intensity is obtained for the structure on u-ZnO with intense LO-like phonon–radiation interaction. The dependence of the emission intensity on temperature and emission window width for various materials shows the effect of material-dependent metal/semiconductor interface conditions on the emission efficiency. [ABSTRACT FROM AUTHOR]

We investigate the one-dimensional tetramerised Kitaev chain induced by imaginary potentials { i γ , − i γ , − i γ , i γ } applied to the dimerised Kitaev chain. It is found that the imaginary potentials cause a variety of topological phase transitions. When the chemical potential μ is tuned to the energy zero point, they lead to the appearance of the mixed phase of the system consisting of two purely real Kitaev-like modes and four purely imaginary energy SSH-like zero-energy modes, which appear as the transition of the Kitaev-like-mixed-SSH-like phase. In addition, the Kitaev-like phase can be broadened by imaginary potentials, manifested as the widening of the quantised Andreev reflection plateau. When μ ≠ 0 , the same topological phase transition occurs, from the topologically-trivial phase to the Kitaev-like phase. One can believe that this work provides theoretical support for probing the generation of Majorana zero modes in new topological superconducting systems. • One-dimensional tetramerised Kitaev chain induced by imaginary potential is proposed. • Imaginary potential leads to mixed phases formed by Kitaev-like and SSH-like phases. • The Kitaev-like phase can be broadened by imaginary potentials. [ABSTRACT FROM AUTHOR]

To investigate hydrogen behaviors in the high-entropy alloy AlCrTiNiV, density functional theory and transition state theory were used to explore the molecular H2 absorption and dissociation and the atomic H adsorption, diffusion, and penetration progress. The H2 molecule, where the H-H band is parallel to the surface layer, is more inclined to absorb on the top site of the Ti atom site of first atomic layer on the AlCrTiNiV surface, then diffuse into the hollow sites, through the bridge site, after dissociating into two H atoms. Atomic H is more likely to be absorbed on the hollow site. The absorption capacity for atomic H on the surface tends to decline with the increase in H coverage. By calculating the energy barriers of atomic H penetration in AlCrTiNiV, it was indicated that lattice distortion may be one important factor that impacts the permeation rate of hydrogen. Our theory research suggests that high-entropy alloys have potential for use as a hydrogen resistant coating material.

We develop a systematic approach to optimize training set sizes for neural networks when fitting ab initio potential energy surfaces. We use the approach to construct several spectroscopic quality potential energy surfaces for [Li(H 2) n ] + , n = 1 − 9. Ground state properties are computed for all the systems and for selected isotopologues. The nuclear quantum effects, produce relatively small zero point energy fractions of the classical binding energy. Evaporating a hydrogen molecule from the pentamer requires 2280 K of energy when the zero point energy contribution is included, making the aggregate thermodynamically stable below 200 K. [Display omitted] • A highly accurate potential energy for lithium ion–hydrogen clusters is optimized. • The structure and ground state properties of clusters are determined. • A systematic cross validation approach for neural networks is presented. [ABSTRACT FROM AUTHOR]

It is postulated that the energy density of the (quantum) vacuum acts firstly as dark energy and secondly as a part of dark matter. Assisted by electric fields arising from a small charge mismatch in the cosmic plasma, it can condense on mass concentrations. No longer participating in the cosmic expansion, this constitutes "electro-aether-energy" (EAE), "electro-zero-point-energy" or "electro-vacuum-energy", which solves the dark matter riddle without new physics. A radial electric field of 1 kV/m is predicted in the Galaxy. For proper electric fields, EAE can cover the results deduced with MOND. An instability allows a speedy filling of dark matter cores. Hydrostatic equilibrium in galaxy clusters is obeyed. Flowing in aether energy of explains why black holes become supermassive, do not have mass gaps and overcome the final parsec problem. Rupture of charged clouds reduces, e.g., the primordial baryon cloud to the cosmic web. The large coherence scale of the electric field acts as a scaffold for gentle galaxy formation and their vast polar structures. In galaxy merging and bars, there occurs no dynamical friction. At cosmological scales, EAE acts as pressureless dark matter. Its amount increases in time, which likely solves the Hubble tension by its late time physics. A big crunch can occur. Of the large cosmological constant injected at the Big Bang, a small part kept that form, without fine-tuning. [ABSTRACT FROM AUTHOR]

The development of novel methods in solid‐state quantum chemistry necessitates reliable reference data sets for their assessment. The most fundamental solid‐state property of interest is the crystal structure, quantified by the lattice parameters. In the last decade, several studies were conducted to assess theoretical approaches based on the agreement of calculated lattice parameters with respect to experiment as a measure. However, most of these studies used a limited number of reference systems with high symmetry. The present work offers a more comprehensive reference benchmark denoted as Sol337LC, which consists of 337 inorganic compounds with 553 symmetry‐inequivalent lattice parameters, representing every element of the periodic table for atomic numbers between 1 and 86, except noble gases, the radioactive elements and lanthanoids. The reference values were taken from earlier benchmarks and from measurements at very low temperature or extrapolation to 0 K. The experimental low‐temperature lattice parameters were then corrected for zero‐point energy effects via the quasi‐harmonic approximation for direct comparison with quantum‐chemical optimized structures. A selection of standard density functional approximations was assessed for their deviations from the experimental reference data. The calculations were performed with the crystal orbital program CRYSTAL23, applying optimized atom‐centered basis sets of triple‐zeta plus polarization quality. The SCAN functional family and the global hybrid functional PW1PW, augmented with the D3 dispersion correction, were found to provide closest agreement with the Sol337LC reference data. [ABSTRACT FROM AUTHOR]

The complex multichannel OH + CH3NH2 reaction is investigated using high-level ab initio methods considering not just the abstraction, but the substitution pathways, too. The H-abstraction channels are proven to be exothermic with classical(adiabatic) relative energies of -25.58(-26.23) and -17.93(-19.32) kcal mol-1 for the methyl- and amino-H-abstraction processes resulting in H2O + CH2NH2 and CH3NH, respectively. There is another reaction path that is thermodynamically favored: the amino-substitution leading to NH2 + CH3 OH with a classical(adiabatic) reaction energy of -6.43(-7.76) kcal mol-1. The H- and methyl-substitution reactions, which provide H + HOCH2NH2/CH3NHOH and CH3 + NH2 OH, respectively, have higher energies relative to the reactants making them endothermic. The entrance channel of the reaction is studied using one-dimensional energy curves where the reactants are frozen in their equilibrium structures and they approach each other from different directions. The geometry optimization of the stationary points, including the reactants, transition states, post-reaction complexes and products, is carried out by the MP2 and CCSD(T)-F12b methods using the aug-cc-pVDZ and aug-cc-pVTZ basis sets. To reach higher chemical accuracy we perform single-point energy calculations at the CCSD(T)-F12b/aug-cc-pVQZ level of theory that are augmented with different energy corrections accounting for post-CCSD(T) correlation, core correlation, scalar relativistic effect, spin--orbit coupling and zero-point energy. Rate coefficients are computed using transition-state theory with Wigner tunneling correction and compared with previous theoretical and experimental data. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Atomic & Molecular Physics (1000-0364) is the property of Journal of Atomic & Molecular Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The reactive singlet state of oxygen (O2) can decay to the triplet ground state nonradiatively in the presence of a solvent. There is a controversy about whether tunnelling is involved in this nonadiabatic spin-crossover process. Semiclassical instanton theory provides a reliable and practical computational method for elucidating the reaction mechanism and can account for nuclear quantum effects such as zero-point energy and multidimensional tunnelling. However, the previously developed instanton theory is not directly applicable to this system because of a branch-point singularity which appears in the flux correlation function. Here we derive a new instanton theory for cases dominated by the singularity, leading to a new picture of tunnelling in nonadiabatic processes. Together with multireference electronic-structure theory, this provides a rigorous framework based on first principles that we apply to calculate the decay rate of singlet oxygen in water. The results indicate a new reaction mechanism that is 27 orders of magnitude faster at room temperature than the classical process through the minimum-energy crossing point. We find significant heavy-atom tunnelling contributions as well as a large temperature-dependent H2O/D2O kinetic isotope effect of approximately 20, in excellent agreement with experiment. Singlet oxygen relaxes in water to its triplet ground state. Here, the authors show that heavy-atom tunnelling speeds up this reaction from time scales longer than the age of the universe to microseconds. [ABSTRACT FROM AUTHOR]

Efficient separation of oxygen and nitrogen from air is a process of great importance for many industrial and medical applications. Two-dimensional (2D) membranes are very promising materials for separation of gases, as they offer enhanced mass transport due to their smallest atomic thickness. In this work, we examine the capacity of graphdiyne (GDY), a new 2D carbon allotrope with regular subnanometric pores, for separating oxygen (16O2) from nitrogen (14N2). A quantum-mechanical model has been applied to the calculation of the transmission probabilities and permeances of these molecules through GDY using force fields based on accurate electronic structure computations. It is found that the 16O2/14N2 selectivity (ratio of permeances) is quite high (e.g., about 106 and 102 at 100 and 300 K, respectively), indicating that GDY can be useful for separation of these species, even at room temperature. This is mainly due to the N2 transmission barrier (∼0.37 eV) which is considerably higher than the O2 one (∼0.25 eV). It is also found that molecular motions are quite confined inside the GDY pores and that, as a consequence, quantum effects (zero-point energy) are significant in the studied processes. Finally, we explore the possibility of 18O2/16O2 isotopologue separation due to these mass-dependent quantum effects, but it is found that the process is not practical since reasonable selectivities are concomitant with extremely small permeances. [ABSTRACT FROM AUTHOR]

The gas-phase reaction Cl + NH3 → HCl + NH2 is a prototypical hydrogen abstraction reaction, whose minimum energy path involves several intermediate complexes. In this work, a full-dimensional, spin–orbit corrected potential energy surface (SOC PES) is constructed for the ground electronic state of the Cl + NH3 reaction. About 52 000 energy points are sampled and calculated at the UCCSD(T)-F12a/aug-cc-pVTZ level, in which the data points located in the entrance channel are spin–orbit corrected. The spin–orbit corrections are predicted by a fitted three-dimensional energy surface from about 7520 energy points in the entrance channel at the level of CASSCF (15e, 11o)/aug-cc-pVTZ. The fundamental-invariant neural network method is utilized to fit the SOC PES, resulting in a total root mean square error of 0.12 kcal mol−1. The calculated thermal rate constants of the Cl + NH3 → HCl + NH2 reaction on the SOC PES with the soft-zero-point energy constraint agree reasonably well with the available experimental values. [ABSTRACT FROM AUTHOR]

Accurate quantum dynamics simulations of nonadiabatic processes are important for studies of electron transfer, energy transfer, and photochemical reactions in complex systems. In this comparative study, we benchmark various approximate nonadiabatic dynamics methods with mapping variables against numerically exact calculations based on the tensor-train (TT) representation of high-dimensional arrays, including TT-KSL for zero-temperature dynamics and TT-thermofield dynamics for finite-temperature dynamics. The approximate nonadiabatic dynamics methods investigated include mixed quantum–classical Ehrenfest mean-field and fewest-switches surface hopping, linearized semiclassical mapping dynamics, symmetrized quasiclassical dynamics, the spin-mapping method, and extended classical mapping models. Different model systems were evaluated, including the spin-boson model for nonadiabatic dynamics in the condensed phase, the linear vibronic coupling model for electronic transition through conical intersections, the photoisomerization model of retinal, and Tully's one-dimensional scattering models. Our calculations show that the optimal choice of approximate dynamical method is system-specific, and the accuracy is sensitively dependent on the zero-point-energy parameter and the initial sampling strategy for the mapping variables. [ABSTRACT FROM AUTHOR]

Triplet–triplet annihilation and singlet fission are bimolecular processes which can be exploited in a range of technological applications. These processes involve the first excited singlet and triplet states (S1 and T1), and have restrictions on their relative energies. While singlet–singlet energy differences are easily measured using optical spectroscopy, the singlet–triplet energy gap is less amenable to experiment. We report a computationally inexpensive method for the calculation of the energy of the lowest singlet–triplet transition for a range of extended π chromophores. Excellent correlation (mean absolute displacement ≲0.05 eV) between experiment and calculation is achieved for a wide range of molecules without requiring zero point energy calculations. This provides the experimental chemist with the necessary tools to accurately predict T1 energies for novel molecules that are candidates for triplet–triplet annihilation or singlet fission. [ABSTRACT FROM AUTHOR]

Perturbative calculations predict that the effective potential of the Standard Model should have a new minimum, well beyond the Planck scale, which is much deeper than the electroweak vacuum. So far, most authors have accepted the metastability scenario in a cosmological perspective which is needed to explain why the theory remains trapped in our electroweak vacuum but requires to control the properties of matter in the extreme conditions of the early universe. As an alternative, one can consider the completely different idea of a non-perturbative effective potential that, as at the beginning of the Standard Model, is restricted to the pure Φ 4 sector but is consistent with the indications of the now existing analytical and numerical studies, namely "triviality" and a description of SSB as weak first-order phase transition. In this approach, the electroweak vacuum is now the lowest energy state because, besides the state with mass m h = 125 GeV, defined by the quadratic shape of the potential at its minimum, there is a second much larger mass scale (M H) Theor ∼ 690 (30) GeV associated with the zero-point energy determining the potential depth. Despite its large mass, the heavier state would couple to longitudinal Ws with the same typical strength as the low-mass state at 125 GeV and thus represent a relatively narrow resonance mainly produced at LHC by gluon-gluon fusion. Therefore, it is interesting that, in the LHC data, one can find combined indications of a new resonance of mass (M H) comb ∼ 685 (10) GeV, with a statistical significance which is far from negligible. Since this non-negligible evidence could become an important new discovery with forthcoming data, we outline further refinements of the theoretical predictions, that could be obtained by implementing unitarity constraints, in the presence of fermion and gauge fields, with the type of coupled-channel calculations nowadays used in meson spectroscopy. [ABSTRACT FROM AUTHOR]

The chemical kinetic studies of hydrogen atom (H-atom) abstraction reactions by hydroperoxyl (HOİ2) radicals from five branched pentanol isomers, including 3-methyl-1-butanol, 2-methyl-1-butanol, 1,1-dimethyl-1-propanol, 1,2-dimethyl-1-propanol, and 2,2-dimethyl-1-propanol were investigated systematically through high-level ab initio calculations. Geometry optimization, frequency analysis, and zero-point energy (ZPE) corrections were performed for six reactants, twenty-three transition states (TSs), and twenty-four products at the M06-2X/6-311++G(d,p) level of theory. The intrinsic reaction coordinate calculation was performed at the same level of theory to confirm the transition state connection. The one-dimensional hindered rotor treatment for low-frequency torsional modes was also treated at the M06-2X/6-311++G(d,p) level of theory. The QCISD(T)/CBS level of theory was used to calculate the single-point energies for the species whose T1 diagnostic value was lower than 0.035. At the same time, the CASPT2/CBS level of theory was used to calculate the single-point energies for the channel in which the T1 diagnostic value of transition states was greater than 0.035. Rate constants for the H-atom abstraction reactions from the five branched pentanol isomers by HOİ2 radicals were calculated by using conventional transition state theory with asymmetric Eckart tunneling corrections in the temperature range of 500–2000 K. Rate constants and branching ratios for the title reactions and the rate rules for ten different H-atom abstraction types were investigated. Temperature-dependent thermochemistry properties for all reactants and products were calculated by the composite methods of G3/G4/CBS-QB3/CBS-APNO, which were in good agreement with the data available in the literature. Rate constants for the H-atom abstraction reactions by HOİ2 radical from branched pentanol isomers were investigated in this work as part I, and those for linear pentanol isomers will be analyzed in part II. All the calculated kinetics and thermochemistry data can be utilized in the model development for branched pentanol isomers oxidation. [ABSTRACT FROM AUTHOR]

The correlation functional holds significance in density functional theory as it addresses electron–electron interactions beyond the mean-field approximation, enhancing the accuracy of total energy calculations, electronic excitations, and the prediction of materials properties. There are several expressions to describe this energy, and each of them has a unique set of errors in calculating particular properties of materials. This work offers a new correlation functional by employing the density's dependence on ionization energy. We theoretically derived this functional and combined it with the previously reported ionization energy dependent exchange functional to investigate its effect on the total energy, bond energy, dipole moment, and zero-point energy of 62 molecules. The comparison of this new functional in respect to existing widely used correlation models including QMC, PBE, B3LYP and Chachiyo models shows how well it works in producing accurate results with minimal mean absolute error. [ABSTRACT FROM AUTHOR]

The 1 : 2 adduct of 1-phenyl-2,2,2-trifluoroethanol (PhTFE), a chiral fluoroalcohol, with two water molecules (PhTFE⋯2H2O) was investigated via chirped pulse Fourier-transform microwave (CP-FTMW) spectroscopy and theoretical calculations. A systematic search of the PhTFE⋯2H2O conformational landscape identified 38 stable minima at the B3LYP-D3BJ/def2-TZVPPD level of theory, 27 of which are within an energy window of 10 kJ mol−1 after applying zero-point energy corrections. Rotational spectra of a single PhTFE⋯2H2O conformer along with eight deuterated and three oxygen-18 isotopologues were assigned. Interestingly, the observed PhTFE⋯2H2O conformer contains PhTFE II, the second most stable monomer conformer, and the most stable PhTFE I dihydrate is ca. 4 kJ mol−1 higher in energy. In contrast, PhTFE I⋯H2O was identified experimentally and theoretically as the most stable 1 : 1 conformer. Furthermore, the observed dihydrate structure experiences large amplitude motions connecting three theoretical minima which differ only in which water oxygen lone pairs are involved in the hydrogen-bonds, i.e., the free OH pointing directions. Additionally, the ortho and para-H2O tunnelling splittings were detected and attributed to the interchange water hydrogen atoms which interact with the aromatic part of PhTFE but not for the water interacting with PhTFE hydroxy group. Extensive theoretical modelling was carried out to gain insight into the associated large amplitude motions including tunnelling, supported by the experimental isotopic and tunnelling splitting data. [ABSTRACT FROM AUTHOR]

We determine benchmark geometries and relative energies for the stationary points of the Cl + CH3X [X = F, Cl, Br, I] reactions. We consider four possible reaction pathways: hydrogen abstraction, hydrogen substitution, halogen abstraction, and halogen substitution, where the substitution processes can proceed via either Walden inversion or front-side attack. We perform geometry optimizations and obtain harmonic vibrational frequencies at the explicitly-correlated UCCSD(T)-F12b/aug-cc-pVTZ level of theory, followed by UCCSD(T)-F12b/aug-cc-pVQZ single-point computations to make finite-basis-set error negligible. To reach chemical (<1 kcal mol−1), or even subchemical (<0.5 kcal mol−1) accuracy, we include core-correlation, scalar relativistic, post-(T), spin–orbit-splitting and zero-point-energy contributions, as well, in the relative energies of all the stationary points. Our benchmark 0 K reaction enthalpies are compared to available experimental results and show good agreement. The stationary-point structures and energetics are interpreted in terms of Hammond's postulate and used to make predictions related to the dynamical behavior of these reactive systems. [ABSTRACT FROM AUTHOR]

Reaction kinetics of hydrogen atom abstraction from six alkyl cyclohexanes, methyl cyclohexane (MCH), ethyl cyclohexane (ECH), n-propyl cyclohexane (nPCH), iso-propyl cyclohexane (iPCH), sec-butyl cyclohexane (sBCH) and iso-butyl cyclohexane (iBCH), by the Hİ atom are systematically studied in this work. The M06-2X method combined with the 6-311++G(d,p) basis set is used to perform geometry optimization, frequency analysis and zero-point energy calculations for all species. The intrinsic reaction coordinate (IRC) calculations are performed to confirm the transition states connecting the reactants and products correctly. One-dimensional hindered rotors are used to treat the low frequency torsional models with potentials scanned at the M06-2X/6-31G level of theory. Electronic single-point energy calculations for all reactants, transition states, and products are performed at the QCISD(T)/CBS level of theory. High-pressure limiting rate constants of 39 reaction channels are obtained using conventional transition state theory with asymmetric Eckart tunneling corrections in the temperature range 298.15–2000 K. Reaction rate rules for H-atom abstraction by the Hİ atom from alkyl cyclohexanes on primary, secondary and tertiary carbon sites on both the side chain and ring are provided. The obtained rate constants are given by the Arrhenius expression in the temperature range 500–2000 K, which can be used for the combustion kinetics model development for alkyl cyclohexanes. [ABSTRACT FROM AUTHOR]

A solid-state experiment based on quantum tunneling is proposed to reproduce the natural numbers and prime numbers as resonant tunneling energies in a double barrier system (DBS). For getting the prime numbers as eigenvalues the well potential is considered as the superposition of a smooth potential which is estimated using a semi-classical approach and a weak local fluctuating potential. We use the transfer matrix approach and finite element method by taking only the smooth part of the potential to obtain resonant energies which reproduces the local average prime density and the local average prime gap exactly. The methodology when applied to a quadratic potential of the well, produces whole numbers as eigenvalues except for a constant zero-point energy —the energy levels of a simple harmonic oscillator. [ABSTRACT FROM AUTHOR]