Internal Vibrational Energy Research Articles

Investigation on the structural, elastic, electronic, thermodynamic, and vibrational properties of the full heusler Sc2XAl (X =Cd and Zn): An ab initio study

The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc2CdAl and Sc2ZnAl in L21 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L21 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc2CdAl and Sc2ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc2CdAl and Sc2ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications.

An environmental impact statement for molecular anions.

A molecular anion's (MA's) chemical reactivity and physical behavior can be quite different when it is surrounded by other molecules than when it exists in isolation. This sensitivity to the surrounding environment is especially high for anions because their outermost valence electrons are typically loosely bound and exist in rather spatially diffuse orbitals, allowing even weak intermolecular interactions arising from the environment to have strong effects. This Perspective offers illustrations of such sensitivity for a variety of cases including (i) the effect of solvation on electron binding energies, (ii) how some "well known" anions need to have solvent molecules around to even exist as stable species, (iii) how internal Coulomb repulsions within a multiply charged MA can provide temporary stability toward electron loss, (iv) how MAs arrange themselves spatially near liquid/vapor interfaces in manners that can produce unusual reactivity, (v) how nearby cationic sites can facilitate electron attachment to form a MA site elsewhere, (vi) how internal vibrational or rotational energy can make a MA detach an electron.

Revealing the ground‐state geometry, optoelectronic, mechanical and thermodynamic behaviors, and efficiency of formamidinium mixed halide perovskites for solar cell applications

Hybrid organic-inorganic lead halide perovskites are the revolutionary materials that have brought a new era of low-cost and highly efficient solar cells. Generally, high-performing perovskite solar cells incorporate formamidinium-based lead halide perovskites. Using density functional theory, we employed generalized gradient approximation (GGA) and meta-GGA (MGGA) exchange-correlation functionals to investigate the structural, electronic, optical, mechanical, and thermodynamic properties of the perovskite series FAPbI3, FAPbBr2I, FAPbBrI2, and FAPbBr3. Both the functionals successfully determined the most stable structure for each mixed halide perovskite. Electronic properties such as band structure, the density of states, and effective masses have been calculated and discussed. Our estimated band gap values using MGGA functional are more close to the experiments than PBE. Optical properties of the perovskite series such as dielectric function, complex refractive index, absorption coefficient, and reflectivity have been explained in the light of photovoltaic applications. Moreover, we predicted the maximum absorber efficiency via the spectroscopic limited maximum efficiency method. FAPbI3 achieved the highest efficiency by virtue of its suitable band gap and maximum absorption. Mechanical properties have also been studied through elastic constants, elastic moduli, Pugh ratio, Poisson ratio, and other several properties, which reveal the declining flexibility of perovskites with bromine. Further, thermodynamic properties like heat capacity, Debye temperature, vibrational internal energy, vibrational entropy, thermal expansion, and thermal stability have been discussed and analyzed. Among all perovskites, the thermodynamic stability of FAPbBr2I is found superior due to strong Br-I bonds and the tougher attraction of the ionic system in the perovskite lattice. All the results are compared with earlier reported values and found to be in fair agreement.

Laser Cooling and Trapping of Rare-Earth-Doped Particles

This review focuses on optical refrigeration with the anti-Stokes fluorescence of rare-earth (RE)-doped low-phonon micro- and nanocrystals. Contrary to bulk samples, where the thermal energy is contained in internal vibrational modes (phonons), the thermal energy of nanoparticles is contained in both the translational motion and internal vibrational (phonons) modes of the sample. Much theoretical and experimental research is currently devoted to the laser cooling of nanoparticles. In the majority of the related work, only the translational energy of the particles has been suppressed. In this review, the latest achievements in hybrid optical refrigeration of RE-doped low-phonon micro- and nanoparticles are presented. Hybrid cooling permits the suppression of not only the translational energy of the RE-doped particles, but also their internal vibrational phonon thermal energy. Laser cooling of nanoparticles is not a simple task. Mie resonances can be used to enhance laser cooling with the anti-Stokes fluorescence of nanoparticles made of low-phonon RE-doped solids. Laser-cooled nanoparticles is a promising tool for fundamental quantum-mechanical studies, nonequilibrium thermodynamics, and precision measurements of forces.

Nonrelativistic solutions of Schrödinger equation and thermodynamic properties with the proposed modified Mobius square plus Eckart potential

We obtain solutions of Schrödinger equation for the modified Mobius square plus Eckart (MMPSE) potential via the formula method. Numerical results are reported. In addition, the partition function Z and other thermodynamic properties such as vibrational free energy, F, vibrational internal energy, U, vibrational entropy, S, and vibrational specific heat, C are presented. We also discuss special cases of this potential. Our result is consistent with previous studies in the literature.

Nonrelativistic treatment of inversely quadratic Hellmann-Kratzer potential and thermodynamic properties

The study presents approximate analytical solutions of the Schrödinger equation with a newly proposed potential model called Inversely Quadratic Hellmann-Kratzer potential (IQHKP). This potential is a superposition of Inversely Quadratic Hellman potential and Kratzer potential. The energy eigenvalues and corresponding wavefunction are calculated via the formula method. We applied our results to evaluate thermodynamic functions such as vibrational free energy, F, vibrational internal energy, U, vibrational entropy, S, and vibrational specific heat, C. We also reported special cases of importance.

Singlet O2 Produced by Ultraviolet Dissociation of the β-ionone-O2 Complex.

We formed the gas-phase β-ionone-O2 complex in a supersonic expansion and then photodissociated the complex with light near 312 nm. Photodissociation resulted in the production of O2 in the a 1Δg state, which was ionized at 312 nm using (2 + 1) resonance-enhanced multiphoton ionization (REMPI). We recorded the 1O2 REMPI action spectrum and O2+ velocity map ion image following photodissociation of the complex. From the velocity map image, we determined the total recoil kinetic energy distribution from dissociation of the complex. Fitting the REMPI spectrum showed that the 1O2 product has an effective rotational temperature of about 50 K, while the recoil kinetic energy distribution was well fit with a statistical Boltzmann distribution having an effective translational temperature of 289 K. Using the average translational energy from the Boltzmann fit along with the complex dissociation energy from ab initio calculations, we determined that β-ionone was formed with an average of 2.87 eV of internal energy, which was 0.49 eV higher than previous measurements for the β-ionone triplet-state energy. Our own CCSD/cc-pVDZ//(U)MP2/cc-pVDZ calculations gave a minimum triplet-state energy of 2.04 eV. However, a large structural change occurs between the minimum singlet-ground-state geometry and the minimum triplet-excited-state geometry, and as a result, the calculated vertical energy for the triplet-state β-ionone was determined to be 3.30 eV. Comparing the ab initio and experimental results indicated that following excitation, β-ionone was formed in the triplet state but with significant internal vibrational energy. As such, complex dissociation likely proceeds following internal vibrational energy redistribution, which explains the statistical recoil kinetic energy distribution.

Photo-induced primary processes of trans-[Co(acac)2(N3)(py)] in liquid solution studied by femtosecond vibrational and electronic spectroscopies

The elementary light-triggered dynamics of the transition metal complex, trans-[CoIII(acac)2(N3)(py)] (trans-[1]), was investigated using femtosecond mid-infrared (mIR) and UV-Vis spectroscopies following ultrafast acetylacetonate-to-cobalt charge-transfer excitation at 266 nm. The spectro-temporal response is indicative of an ultrafast return to the electronic ground state via a sequential intramolecular electron transfer. The locally excited ligand-to-metal charge transfer state, 1LMCTacac, decays within 200 fs via azide-to-acac electron transfer to another charge-transfer state, 1LMCTazide, that features an azidyl radical ligand attached to a cobalt(II) center. A subsequent cobalt-to azidyl electron transfer occurring within 1.8 ps generates an excited metal centered state, 1MC, thereby re-establishing the fully closed-shell character of the anionic azido and acac ligands. The fully relaxed electronic ground state of trans-[1] is then recovered via internal conversion and vibrational energy relaxation on a 10 ps-time scale.

Vibrational Internal Energy And Helmholtz Free Energy Of Metals

This article revealed an interesting issue on vibrational internal energy and Helmholtz free energy of metals. The relationship existing between the lateral strain and axial strain was taking into consideration during computation. Vibrational internal energy and Helmholtz free energy of metals was computed and studied based on the theory of free electron approximation using the knowledge of thermodynamic potentials. Computed and theoretically obtained experimental valueof vibrational internal energy and Helmholtz free energy of metals agreed quite well with each other.Vibrational internal energy of metals increases as temperature increasesdue to change in atomic configuration mode and valence electron exchange between ions in metals.Increase in vibrational internal energy of metals as strain increases can be caused by weak electron cohesion and uncertainties regarding the behavior of valence electrons, atomic size, atomic configuration and bonding interaction between the electron in metals. Result obtained for free energy of metals is negative throughout which indicate that there is a better binding between electron in metals. Free energy of metals decreases as temperature increases due to reduction in atomic interaction and bond strength between the interacting electron in metals. Free energy of metals decreases as strain increases.

Propensity for super energy transfer as a function of collision energy for the H + C2H2 system

In a super energy transfer process, a significant portion of the initial relative collision energy can be transferred to the internal vibrational energy of the target molecule through chemical complex formation. The phenomenon of super energy transfer for the H + C2H2 system is investigated in a collision energy region from 25 to 65 kcal/mol. Based on the quasi-classical trajectory calculations, it has been found that the super energy transfer can occur for all the collision energies considered. The chemical-complex-formation mechanism plays an essential role for the super energy transfer process. Additionally, the average energy transfer increases almost linearly with the collision energy.

First Principles calculations of structural, electronic, elastic, vibrational, and thermodynamic properties of TMPs compounds (TM= Cr, Mo)

The structural, electronic, elastic, vibrational, and thermodynamic properties of transitions metal phosphides TMP with (TM = Cr and Mo) in zinc blende (ZB) structure are investigated in the framework of density functional theory (DFT) implemented in QUANTUM ESPRESSO. The obtained results show that TMP are stable in the ferromagnetic (FM) phase. The obtained results of lattice parameter are in good agreement with available results. The density of states (DOS) and bands structures with GGA approach show that TMP have a metallic behavior, whereas with GGA + U CrP becomes half-metallic, while MoP retains a metallic behavior. The calculated phonon frequencies of TMP are positives reflect the dynamical stability of these compounds in cubic ZB structure. Elastic constants of TMP satisfied the Born- Huang stability criteria. The bulk modulus, shear modulus, anisotropy factor, Young’s modulus, Poisson’s ratio, Pugh’s ratio, the sound velocity and Debye temperature are also investigated and indicate that these compounds have ductility and anisotropic behaviors. The thermodynamic properties such as vibrational free energy, internal energy, entropy, and volume-constant heat capacity are also studied.

Analytical solutions of fractional Schrödinger equation and thermal properties of Morse potential for some diatomic molecules

By employing the concept of conformable fractional Nikiforov–Uvarov (NU) method, we solved the fractional Schrödinger equation with the Morse potential in one dimension. The analytical expressions of the bound state energy eigenvalues and eigenfunctions for the Morse potential were obtained. Numerical results for the energies of Morse potential for the selected diatomic molecules were computed for different fractional parameters chosen arbitrarily. Also, the graphical variation of the bound state energy eigenvalues of the Morse potential for hydrogen dimer with vibrational quantum number and the range of the potential were discussed, with regards to the selected fractional parameters. The vibrational partition function and other thermodynamic properties such as vibrational internal energy, vibrational free energy, vibrational entropy and vibrational specific heat capacity were evaluated in terms of temperature. Our results are new and have not been reported in any literature before.

Size-dependent velocity distributions and temperatures of metal clusters in a helium carrier gas

Combining a laser vaporization cluster source, a velocity scan system, and a time-of-flight mass spectrometer, we measured velocity distributions of few-atom cobalt clusters (${\text{Co}}_{n}, n=6--60$) suspended in a helium carrier gas and expanded into vacuum. The velocity distributions provide information about the cluster size dependence of the translational temperature, flow velocity, and velocity slip with respect to the helium carrier gas. The system of clusters in a carrier gas is found to violate the equipartition theorem. Although the clusters in the expansion do not thermalize with the helium gas, they do experience significant, size-dependent internal cooling. While expanding into vacuum, the clusters collide, at least a couple of hundred times, superelastically with the carrier gas, thereby transferring internal vibrational energy into self-acceleration and increasing the flow velocity of the gas as a whole. It is also demonstrated that the proposed velocity distribution measurements can be used to test whether a source produces thermalized clusters.

Energies Spectra and Thermodynamic Properties of Hyperbolic Pöschl–Teller Potential (HPTP) Model

We solved the Dirac equation using modified factorization method with hyperbolic Poschl–Teller potential model. Relativistic and non-relativistic ro-vibrational energy spectra were obtained and numerical solutions for four diatomic molecules $$\left( {{\text{HCl}},\;{\text{H}}_{2} ,\;{\text{CO}}\;{\text{and}}\;{\text{LiH}}} \right)$$ obtained also. The eigenfunction for this potential has been obtained in terms of hypergeometric function. The energy variations with different potential parameters and quantum numbers of the hyperbolic Poschl–Teller potential are also plotted. In addition, we evaluate the vibrational partition function and other thermodynamic properties such as vibrational internal energy, vibrational free energy, vibrational entropy and vibrational specific heat capacity, in terms of temperature and upper bound vibration quantum number. Our results are consistent with those found in the available literature.

Lattice dynamics of Pnma Sn(S1–xSex) solid solutions: energetics, phonon spectra and thermal transport

Alloying is widely used as a means to fine-tune the properties of thermoelectric materials by reducing the lattice thermal conductivity. However, the effects of compositional variation on the lattice dynamics of alloy systems are not well understood, due in part to the difficulty of building realistic first-principles models of structurally-complex solid solutions. This work builds on our previous study of Snn(S1–xSex)m solid solutions (Gunn et al 2019 Chem. Mater. 31 3672) to explore the lattice dynamics of the Pnma Sn(S1–xSex) system, which has been widely studied for potential thermoelectric applications. We find that the vibrational internal energy and entropy have a large quantitative impact on the mixing free energy and are likely to be particularly important in alloy systems with competing phases. The thermodynamically-averaged phonon dispersions and density of states curves show that alloying preserves the structure of the low-frequency bands of modes associated with the Sn sublattice but broadens the high-frequency chalcogen bands into a near-continuous spectrum at the 50/50 mixed composition. This results in a general reduction in the phonon mode group velocities and an increase in the number of energy-conserving scattering channels for heat-carrying low-frequency modes, which is consistent with the decrease in thermal conductivity observed in experimental measurements. Finally, we discuss some of the limitations of our first-principles modelling approach and propose methods to address these in future studies.

In situstudy of theα-Sn toβ-Sn phase transition in low-dimensional systems: Phonon behavior and thermodynamic properties

The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ to $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase transition using nuclear inelastic x-ray scattering. The vibrational entropy and internal energy per atom as a function of temperature are obtained by numerical integration of the phonon density of states. The free energy as a function of temperature for the nanoscale samples is compared to the free energy obtained from ab initio calculations of bulk tin in the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase. In thin films this phase transition is governed by the interplay between the vibrational behavior of the film (the phase transition is driven by the vibrational entropy) and the stabilizing influence of the substrate (which depends on the film thickness). This brings a deeper understanding of the role of lattice vibrations in the phase transition of nanoscale Sn.

Fusion of Ultraviolet-Visible and Infrared Transient Absorption Spectroscopy Data to Model Ultrafast Photoisomerization.

Ultrafast photoisomerization reactions generally start at a higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which are difficult to investigate with a single transient absorption spectroscopy technique, be it in the ultraviolet-visible (UV-vis) or infrared (IR) domain. On one hand, the information available in the UV-vis domain is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling. These limitations can be circumvented by fusing UV-vis and IR transient absorption spectroscopy data in a multiset multivariate curve resolution analysis. We apply this approach to describe the spectrodynamics of the ultrafast cis-trans photoisomerization around the C-N double bond observed for aromatic Schiff bases. Twisted intermediate states could be elucidated, and isomerization was shown to occur through a continuous complete rotation. More broadly, data fusion can be used to rationalize a vast range of ultrafast photoisomerization processes of interest in photochemistry.

Computing Free Energies of Hydroxylated Silica Nanoclusters: Forcefield versus Density Functional Calculations

We assess the feasibility of efficiently calculating accurate thermodynamic properties of (SiO2)n·(H2O)m nanoclusters, using classical interatomic forcefields (FFs). Specifically, we use a recently parameterized FF for hydroxylated bulk silica systems (FFSiOH) to calculate zero-point energies and thermal contributions to vibrational internal energy and entropy, in order to estimate the free energy correction to the internal electronic energy of these nanoclusters. The performance of FFSiOH is then benchmarked against the results of corresponding calculations using density functional theory (DFT) calculations employing the B3LYP functional. Results are reported first for a set of (SiO2)n·(H2O)m clusters with n = 4, 8 and 16, each possessing three different degrees of hydroxylation (R = m/n): 0.0, 0.25 and 0.5. Secondly, we consider five distinct hydroxylated nanocluster isomers with the same (SiO2)16·(H2O)4 composition. Finally, the free energies for the progressive hydroxylation of three nanoclusters with R = 0–0.5 are also calculated. Our results demonstrate that, in all cases, the use of FFSiOH can provide estimates of thermodynamic properties with an accuracy close to that of DFT calculations, and at a fraction of the computational cost.

Nonlinear vibration absorption for a flexible arm via a virtual vibration absorber

A semi-active vibration absorption method is put forward to attenuate nonlinear vibration of a flexible arm based on the internal resonance. To maintain the 2:1 internal resonance condition and the desirable damping characteristic, a virtual vibration absorber is suggested. It is mathematically equivalent to a vibration absorber but its frequency and damping coefficients can be readily adjusted by simple control algorithms, thereby replacing those hard-to-implement mechanical designs. Through theoretical analyses and numerical simulations, it is proven that the internal resonance can be successfully established for the flexible arm, and the vibrational energy of flexible arm can be transferred to and dissipated by the virtual vibration absorber. Finally, experimental results are presented to validate the theoretical predictions. Since the proposed method absorbs rather than suppresses vibrational energy of the primary system, it is more convenient to reduce strong vibration than conventional active vibration suppression methods based on smart material actuators with limited energy output. Furthermore, since it aims to establish an internal vibrational energy transfer channel from the primary system to the vibration absorber rather than directly respond to external excitations, it is especially applicable for attenuating nonlinear vibration excited by unpredictable excitations.

First-principles investigation on thermal properties and infrared spectra of imperfect graphene

In this study we used first-principles density functional theory to investigate the thermal and optical properties of graphene. Graphene phonon properties were first calculated by the density-functional perturbation theory and then used to acquire thermal properties such as the specific heat, free and total energy, and entropy, as well as the infrared and Raman spectra. Results show that the peaks of phonon density of states at about 40 and 45.5THz in the perfect graphene (G) were shifted to 40.5 and 46THz in the imperfect graphene (G-D), respectively. There are peaks at 16.5, 19, 25, and 43.5THz in the G-D curve, while there is no obvious peak at same frequencies in that of the G. The specific heat and entropy are lower for the G-D than for the G at temperature >280K, but the tendency is slightly reversed at temperature <200K. The total energy, change in vibrational internal energy, and change in the vibrational Helmholtz free energy are all lower for the G-D than for the G. The Helmholtz free energy for the G-D is higher at temperature >1300K, but lower at temperature below 1250K than for the G. In the infrared (IR) spectrum, no absorption peak exists for perfect graphene, but strong absorption is found at about 233, 830 and 1392cm−1 for the G-D. The character peak of sp2 carbon atom in-plane vibration in the Raman spectrum is shifted from 1589cm−1 for the G to 1530cm−1 for the G-D. The defects in the G-D caused the peaks and splits in the IR and Raman spectra.