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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

AI-powered exploration of molecular vibrations, phonons, and spectroscopy

The vibrational dynamics of molecules and solids play a critical role in defining material properties, particularly their thermal behaviors. However, theoretical calculations of these dynamics are often computationally intensive, while experimental approaches can be technically complex and resource-demanding. Recent advancements in data-driven artificial intelligence (AI) methodologies have substantially enhanced the efficiency of these studies. This review explores the latest progress in AI-driven methods for investigating atomic vibrations, emphasizing their role in accelerating computations and enabling rapid predictions of lattice dynamics, phonon behaviors, molecular dynamics, and vibrational spectra. Key developments are discussed, including advancements in databases, structural representations, machine-learning interatomic potentials, graph neural networks, and other emerging approaches. Compared to traditional techniques, AI methods exhibit transformative potential, dramatically improving the efficiency and scope of research in materials science. The review concludes by highlighting the promising future of AI-driven innovations in the study of atomic vibrations.

Han, Bowen [Oak Ridge National Laboratory (ORNL), ↗
DOE OSTI2024

Vibrational properties of heme-nitrosoalkane complexes in comparison with those of their HNO analogs, and reactivity studies towards nitric oxide and Lewis acids

C-Nitroso compounds (RNO, R = alkyl and aryl) are byproducts of drug metabolism and bind to heme proteins, and their heme-RNO adducts are isoelectronic to ferrous nitroxyl (NO-/HNO) complexes. Importantly, heme-HNO compounds are key intermediates in the reduction of NO to N 2 O and nitrite to ammonium in the nitrogen cycle. Ferrous heme-RNO complexes act as stable analogs of these species, potentially allowing for the investigation of the vibrational and electronic properties of unstable heme-HNO intermediates. In this paper, a series of six-coordinate ferrous heme-RNO complexes (where R = iPr and Ph) were prepared using the TPP 2- and 3,5-Me-BAFP 2- co-ligands, and tetrahydrofuran, pyridine, and 1-methylimidazole as the axial ligands (bound trans to RNO). These complexes were characterized using different spectroscopic methods and X-ray crystallography. The complex [Fe(TPP)(THF)(iPrNO)] was further utilized for nuclear resonance vibrational spectroscopy (NRVS), allowing for the detailed assignment of the Fe–N(R)O vibrations of a heme-RNO complex for the first time. The vibrational properties of these species were then correlated with those of their HNO analogs, using DFT calculations. Our studies support previous findings that RNO ligands in ferrous heme complexes do not elicit a significant trans effect. In addition, the complexes are air-stable, and do not show any reactivity of their RNO ligands towards NO. So although ferrous heme-RNO complexes are suitable structural and electronic models for their HNO analogs, they are unsuitable to model the reactivity of heme-HNO complexes. We further investigated the reaction of our heme-RNO complexes with different Lewis acids. Here, [Fe(TPP)(THF)(iPrNO)] was found to be unreactive towards Lewis acids. In contrast, [Fe(3,5-Me-BAFP)(iPrNO) 2 ] is reactive towards all of the Lewis acids investigated here, but in most cases the iron center is simply oxidized, resulting in the loss of the iPrNO ligand. In the case of the Lewis acid B 2 (pin) 2 , the reduced product [Fe(3,5-Me-BAFP)(iPrNH 2 )(iPrNO)] was identified by X-ray crystallography.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrafast vibrational dynamics of a trigonal planar anionic probe in ionic liquids (ILs): A two-dimensional infrared (2DIR) spectroscopic investigation

A major impediment limiting the widespread application of ionic liquids (ILs) is their high shear viscosity. Incorporation of a tricyanomethanide (TCM - ) anion in ILs leads to low shear viscosity and improvement of several characteristics suitable for large scale applications. However, properties including interactions of TCM - with the local environment and dynamics of TCM - have not been thoroughly investigated. Herein, we have studied the ultrafast dynamics of TCM - in several imidazolium ILs using linear IR and two-dimensional infrared spectroscopy techniques. The spectral diffusion dynamics of the CN stretching modes of TCM - in all ILs exhibit a nonexponential behavior with a short time component of ~2 ps and a long time component spanning ~9 ps to 14 ps. The TCM - vibrational probe reports a significantly faster relaxation of ILs compared to those observed previously using linear vibrational probes, such as thiocyanate and selenocyanate. Our results indicate a rapid relaxation of the local ion-cage structure embedding the vibrational probe in the ILs. The faster relaxation suggests that the lifetime of the local ion-cage structure decreases in the presence of TCM - in the ILs. Linear IR spectroscopic results show that the hydrogen-bonding interaction between TCM - and imidazolium cations in ILs is much weaker. Shorter ion-cage lifetimes together with weaker hydrogen-bonding interactions account for the low shear viscosity of TCM - based ILs compared to commonly used ILs. In addition, this work demonstrates that TCM - can be used as a potential vibrational reporter to study the structure and dynamics of ILs and other molecular systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The role of resonant nuclear modes in vibrationally assisted energy transport: The LHCII complex

In this paper, we discuss the explicit role of resonant nuclear/vibrational modes in mediating energy transport among chlorophylls in the Light-harvesting Complex II (LHCII), the major light-harvesting complex in green plants. The vibrational modes are considered to be resonant/quasi-resonant with the energy gap between electronic excitons. These resonant vibrations, along with the remaining nuclear degrees of freedom, constitute the environment/bath to the electronically excited system and contribute to two major phenomena: (a) decoherence and (b) incoherent phonon-mediated population relaxation. In this work, we explore the subtle interplay among the electronic excitation, the resonant vibrations, and the environment in dictating environment assisted quantum transport in light-harvesting complexes. We conclusively show that resonant vibrations are capable of boosting the incoherent population relaxation pathways and cause rapid decoherence.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Two-dimensional electronic–vibrational spectroscopy: Exploring the interplay of electrons and nuclei in excited state molecular dynamics

Two-dimensional electronic-vibrational spectroscopy (2DEVS) is an emerging spectroscopic technique which exploits two different frequency ranges for the excitation (visible) and detection (infrared) axes of a 2D spectrum. In contrast to degenerate 2D techniques, such as 2D electronic or 2D infrared spectroscopy, the spectral features of a 2DEV spectrum report cross correlations between fluctuating electronic and vibrational energy gaps rather than autocorrelations as in the degenerate spectroscopies. The center line slope of the spectral features reports on this cross correlation function directly and can reveal specific electronic-vibrational couplings and rapid changes in the electronic structure, for example. The involvement of the two types of transition moments, visible and infrared, makes 2DEVS very sensitive to electronic and vibronic mixing. 2DEV spectra also feature improved spectral resolution, making the method valuable for unraveling the highly congested spectra of molecular complexes. The unique features of 2DEVS are illustrated in this paper with specific examples and their origin described at an intuitive level with references to formal derivations provided. Although early in its development and far from fully explored, 2DEVS has already proven to be a valuable addition to the tool box of ultrafast nonlinear optical spectroscopy and is of promising potential in future efforts to explore the intricate connection between electronic and vibrational nuclear degrees of freedom in energy and charge transport applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Valence shell photoelectron angular distributions and vibrationally resolved spectra of imidazole: A combined experimental–theoretical study

Linearly polarized synchrotron radiation has been used to record polarization dependent valence shell photoelectron spectra of imidazole in the photon energy range 21–100 eV. These have allowed the photoelectron angular distributions, as characterized by the anisotropy parameter β, and the electronic state intensity branching ratios to be determined. Complementing these experimental data, theoretical photoionization partial cross sections and β-parameters have been calculated for the outer valence shell orbitals. The assignment of the structure appearing in the experimental photoelectron spectra has been guided by vertical ionization energies and spectral intensities calculated by various theoretical methods that incorporate electron correlation and orbital relaxation. Strong orbital relaxation effects have been found for the 15a', nitrogen lone-pair orbital. The calculations also predict that configuration mixing leads to the formation of several low-lying satellite states. The vibrational structure associated with ionization out of a particular orbital has been simulated within the Franck–Condon model using harmonic vibrational modes. The adiabatic approximation appears to be valid for the X 2A" state, with the β-parameter for this state being independent of the level of vibrational excitation. However, for all the other outer valence ionic states, a disparity occurs between the observed and the simulated vibrational structure, and the measured β-parameters are at variance with the behavior expected at the level of the Franck–Condon approximation. Furthermore, these inconsistencies suggest that the excited electronic states may be interacting vibronically such that the nuclear dynamics occur over coupled potential energy surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Long-range model of vibrational autoionization in core-nonpenetrating Rydberg states of NO

In high orbital angular momentum (ℓ ≥ 3) Rydberg states, the centrifugal barrier hinders the close approach of the Rydberg electron to the ion-core. As a result, these core-nonpenetrating Rydberg states can be well described by a simplified model in which the Rydberg electron is only weakly perturbed by the long-range electric properties (i.e., multipole moments and polarizabilities) of the ion-core. We have used a long-range model to describe the vibrational autoionization dynamics of high-ℓ Rydberg states of nitric oxide (NO). In particular, our model explains the extensive angular momentum exchange between the ion-core and the Rydberg electron that had been previously observed in vibrational autoionization of f (ℓ = 3) Rydberg states. These results shed light on a long-standing mechanistic question around these previous observations and support a direct, vibrational mechanism of autoionization over an indirect, predissociation-mediated mechanism. In addition, our model correctly predicts newly measured total decay rates of g (ℓ = 4) Rydberg states because for ℓ ≥ 4, the non-radiative decay is dominated by autoionization rather than predissociation. We examine the predicted NO + ion rotational state distributions generated by vibrational autoionization of g states and discuss applications of our model to achieve quantum state selection in the production of molecular ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Vibrational heat-bath configuration interaction with semistochastic perturbation theory using harmonic oscillator or VSCF modals

Vibrational heat-bath configuration interaction (VHCI)—a selected configuration interaction technique for vibrational structure theory—has recently been developed in two independent works [J. H. Fetherolf and T. C. Berkelbach, J. Chem. Phys. 154, 074104 (2021); A. U. Bhatty and K. R. Brorsen, Mol. Phys. 119, e1936250 (2021)], where it was shown to provide accuracy on par with the most accurate vibrational structure methods with a low computational cost. Here, we eliminate the memory bottleneck of the second-order perturbation theory correction using the same (semi)stochastic approach developed previously for electronic structure theory. This allows us to treat, in an unbiased manner, much larger perturbative spaces, which are necessary for high accuracy in large systems. Stochastic errors are easily controlled to be less than 1 cm−1. We also report two other developments: (i) we propose a new heat-bath criterion and an associated exact implicit sorting algorithm for potential energy surfaces expressible as a sum of products of one-dimensional potentials; (ii) we formulate VHCI to use a vibrational self-consistent field (VSCF) reference, as opposed to the harmonic oscillator reference configuration used in previous reports. Our tests are done with quartic and sextic force fields, for which we find that with VSCF, the minor improvements to accuracy are outweighed by the higher computational cost associated the matrix element evaluations. We expect VSCF-based VHCI to be important for more general potential representations, for which the harmonic oscillator basis function integrals are no longer analytic.

Chemistry↗
DOE OSTI2023

Pitfalls in the n -mode representation of vibrational potentials

Simulations of anharmonic vibrational motion rely on computationally expedient representations of the governing potential energy surface. The n-mode representation (n-MR)—effectively a many-body expansion in the space of molecular vibrations—is a general and efficient approach that is often used for this purpose in vibrational self-consistent field (VSCF) calculations and correlated analogues thereof. In the present analysis, a lack of convergence in many VSCF calculations is shown to originate from negative and unbound potentials at truncated orders of the n-MR expansion. For cases of strong anharmonic coupling between modes, the n-MR can both dip below the true global minimum of the potential surface and lead to effective single-mode potentials in VSCF that do not correspond to bound vibrational problems, even for bound total potentials. The present analysis serves mainly as a pathology report of this issue. Furthermore, this insight into the origin of VSCF non-convergence provides a simple, albeit ad hoc, route to correct the problem by “painting in” the full representation of groups of modes that exhibit these negative potentials at little additional computational cost. Somewhat surprisingly, this approach also reasonably approximates the results of the next-higher n-MR order and identifies groups of modes with particularly strong coupling. The method is shown to identify and correct problematic triples of modes—and restore SCF convergence—in two-mode representations of challenging test systems, including the water dimer and trimer, as well as protonated tropine.

Chemistry↗
DOE OSTI2023

Resonant interactions involving local vibrational modes in crystals

When an impurity with a light mass is inserted into a crystal, it can undergo a high-frequency oscillation referred to as a local vibrational mode (LVM). A Fermi resonance may occur between the LVM and lower-frequency modes of the defect. The LVM may also interact with phonons or the electromagnetic field. Understanding these interactions can help model and control diffusion, defect reactions, and thermal conductivity. LVMs have been probed in semiconductors using pressure and alloying as experimental parameters, resulting in anticrossing between localized and extended vibrational modes. Furthermore, these types of vibrational interactions could play an important role in the stability and thermal properties of organic–inorganic hybrid semiconductors. The coupling between an LVM and electromagnetic wave yields an “LVM polariton,” an excitation that has significant vibrational and electric-field amplitudes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1′-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3′,5′-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.

Chemistry↗
DOE OSTI2025

Tunable phase-change metasurfaces coupled with mid-infrared molecular vibrations

Chiral optical metasurfaces have emerged as a promising platform in coupling with molecular vibrational fingerprints through the enhanced light-matter interaction under different circularly polarized light illumination. Here, this work reports the mode coupling between the mid-infrared phonon vibrations of polymethyl methacrylate (PMMA) molecules and the thermally tunable chiral metasurfaces based on the phase-change material Ge₂Sb₂Te₅ (GST-225). Phase-change chiral metasurfaces with high circular dichroism (CD) in absorption and tunable plasmonic resonance in the frequency range of 48–56 THz are demonstrated, which covers the phonon vibrational frequency of PMMA molecules at 52 THz. The mode splitting features are observed in the absorption and CD spectra when the metasurface resonance is tuned across the phonon vibrational frequency of PMMA molecules during the phase transition of GST-225. The underlying mechanism of molecule-metasurface coupling is further revealed by studying the electric field and power loss density distributions of the phonon–plasmon coupled modes under both left-handed and right-handed circularly polarized (LCP and RCP) light. The demonstrated results show the potential of dynamically tunable chiral metasurfaces for the applications in label-free molecular sensing, biomedical diagnostics, thermal imaging, and mid-infrared photonics.

Tang, Haotian [Missouri Univ. of Science and Techn↗
DOE OSTI2025

Simultaneous imaging of vibrational, rotational, and electronic wave-packet dynamics in a triatomic molecule

Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Furthermore, our results demonstrate that multicoincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.

Atomic & molecular processes in external fields↗
DOE OSTI2020

Coherent electronic-vibrational dynamics in deuterium bromide probed via attosecond transient-absorption spectroscopy

Ultrafast laser excitation can trigger multiplex coherent dynamics in molecules. Here, we report attosecond transient-absorption experiments addressing simultaneous probing of electronic and vibrational dynamics in a prototype molecule, deuterium bromide (DBr), following its strong-field ionization. Electronic and vibrational coherences in the ionic X$^2\Pi_{3/2}$ and X$^2\Pi_{1/2}$ states are characterized in the Br-$3d$ core-level absorption spectra via quantum beats with 12.6-fs and 19.9-fs periodicities, respectively. Polarization scans reveal that the phase of the electronic quantum beats depends on the probe direction, experimentally showing that the coherent electronic motion corresponds to the oscillation of the hole density along the ionization-field direction. The vibrational quantum beats are found to maintain a relatively constant amplitude, whereas the electronic quantum beats exhibit a partial decrease in time. Quantum wave-packet simulations show that the decoherence effect from the vibrational motion is insignificant because of the parallel relation between the X$^2\Pi_{3/2}$ and X$^2\Pi_{1/2}$ potentials. Finally, a comparison between the DBr and HBr results suggests that rotation motion is responsible for the decoherence since it leads to initial alignment prepared by the strong-field ionization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Vibrational Cooper minima used to verify the dissociation pathway induced by a short intense laser pulse

Vibrational Cooper minima due to weak dipole coupling were previously observed in strong-field dissociation of H 2⁡ + as minima in the kinetic-energy-release (KER) spectrum [McKenna et al., Phys. Rev. Lett. 103, 103006 (2009)]. We demonstrate in two independent experiments that these vibrational Cooper minima occur more generally and can be used as “fingerprints” to identify the final electronic state in the dissociation pathway. In the first experiment, we show the wavelength dependence of the vibrational Cooper minima observed in the KER spectrum of O 2⁢ + dissociation induced by 396- and 264-nm photons. These minima appear at the locations predicted by our first-order perturbation-theory calculations. In the second experiment, a delay-dependent KER spectrum is obtained from O 2 using an ionizing pump and a dissociating probe, then Fourier-transformed to generate a spin-rotation quantum beat spectrum of O 2 ⁢+ . As a result, this spectrum shows vibrational Cooper minima at the expected locations, confirming their presence in another observable. In this case, these minima are used to identify the dissociation pathway.

Molecular dissociation↗
DOE OSTI2023

Optical conductivity and vibrational spectra of the narrow-gap semiconductor FeGa 3

Intermetallic narrow-gap semiconductors have been intensively explored due to their large thermoelectric power at low temperatures and a possible role of strong electronic correlations in their unusual thermodynamic and transport properties. Here we study the optical spectra and vibrational properties of FeGa 3 . The optical conductivity indicates that FeGa 3 has a direct band gap of ≈ 0.7 eV, consistent with density functional theory (DFT) calculations. Most importantly, we find a substantial spectral weight also below 0.4 eV, which is the energy of the indirect (charge) gap found in resistivity measurements and ab initio calculations. We find that the spectral weight below the gap decreases with increasing temperature, which indicates that it originates from the impurity states and not from the electronic correlations. Interestingly, we did not find any signatures of the impurity states in vibrational spectra. The infrared and Raman vibrational lines are narrow and weakly temperature dependent. The vibrational frequencies are in excellent agreement with our DFT calculations, implying a modest role of electronic correlations. Narrow Mössbauer spectral lines also indicate high crystallinity of the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Effect of interfacial vibrational coupling on surface wettability and water transport

Here, we report that the atomic-scale vibrational coupling at the solid-fluid interface can substantially alter the interfacial properties such as wettability and fluid slip. The wettability of water droplets on substrates subjected to various vibrational frequencies is studied using molecular dynamics simulation. The contact angle increases (i.e., becomes more hydrophobic) when the oscillation frequency of the substrate matches the intermolecular bending frequency of liquid water. We investigate the underlying mechanism by examining the dynamics of water molecules at the interface and find that the temporal contact between the solid and fluid is shorter when the frequencies match, resulting in weak solid-fluid adsorption. We further report that the vibrational match at the interface reduces wall-fluid friction and enhances water transport through the nanopore. Our findings demonstrate the importance of the atomic-scale vibrational coupling at the solid-fluid interface on the physicochemical behavior of nanodevices and biological nanochannels.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Quantum computation solves a half-century-old enigma: Elusive vibrational states of magnesium dimer found

The high-lying vibrational states of the magnesium dimer (Mg 2 ), which has been recognized as an important system in studies of ultracold and collisional phenomena, have eluded experimental characterization for half a century. Until now, only the first 14 vibrational states of Mg 2 have been experimentally resolved, although it has been suggested that the ground-state potential may support five additional levels. Here, we present highly accurate ab initio potential energy curves based on state-of-the-art coupled-cluster and full configuration interaction computations for the ground and excited electronic states involved in the experimental investigations of Mg 2 . Our ground-state potential unambiguously confirms the existence of 19 vibrational levels, with ~1 cm -1 root mean square deviation between the calculated rovibrational term values and the available experimental and experimentally derived data. Our computations reproduce the latest laser-induced fluorescence spectrum and provide guidance for the experimental detection of the previously unresolved vibrational levels.

74 ATOMIC AND MOLECULAR PHYSICS↗