scholarly journals Between Harmonic Crystal and Glass: Solids with Dimpled Potential-Energy Surfaces Having Multiple Local Energy Minima

Crystals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 84
Author(s):  
Nikolai A. Zarkevich ◽  
Duane D. Johnson
Keyword(s):  
Potential Energy ◽  
Symmetry Breaking ◽  
Potential Energy Surfaces ◽  
Density Wave ◽  
Wave System ◽  
Fixed Temperature ◽  
Anharmonic Vibrations ◽  
Theoretical Predictions ◽  
Energy Surfaces ◽  
Layered Charge

Solids with dimpled potential-energy surfaces are ubiquitous in nature and, typically, exhibit structural (elastic or phonon) instabilities. Dimpled potentials are not harmonic; thus, the conventional quasiharmonic approximation at finite temperatures fails to describe anharmonic vibrations in such solids. At sufficiently high temperatures, their crystal structure is stabilized by entropy; in this phase, a diffraction pattern of a periodic crystal is combined with vibrational properties of a phonon glass. As temperature is lowered, the solid undergoes a symmetry-breaking transition and transforms into a lower-symmetry phase with lower lattice entropy. Here, we identify specific features in the potential-energy surface that lead to such polymorphic behavior; we establish reliable estimates for the relative energies and temperatures associated with the anharmonic vibrations and the solid–solid symmetry-breaking phase transitions. We show that computational phonon methods can be applied to address anharmonic vibrations in a polymorphic solid at fixed temperature. To illustrate the ubiquity of this class of materials, we present a range of examples (elemental metals, a shape-memory alloy, and a layered charge-density-wave system); we show that our theoretical predictions compare well with known experimental data.

The lithium superoxide radical: Symmetry breaking phenomena and potential energy surfaces

1989 ◽  
Vol 133 (1) ◽  
pp. 11-45 ◽  
Author(s):  
Wesley D. Allen ◽  
David A. Horner ◽  
Roger L. Dekock ◽  
Richard B. Remington ◽  
Henry F. Schaefer
Keyword(s):  
Potential Energy ◽  
Symmetry Breaking ◽  
Potential Energy Surfaces ◽  
Superoxide Radical ◽  
Energy Surfaces ◽  
Symmetry Breaking Phenomena

scholarly journals Diagonal Born-Oppenheimer Corrections to the Ground Electronic State Potential Energy Surfaces of Ozone: Improvement of Ab Initio Vibrational Band Centers for the 16O3, 17O3 and 18O3 Isotopologues

2020 ◽  
Author(s):  
Attila Tajti ◽  
Péter Szalay ◽  
Roman V. Kochanov ◽  
Vladimir G. Tyuterev
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Potential Energy Surfaces ◽  
Vibrational States ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
State Potential ◽  
Effective Models ◽  
Energy Surfaces ◽  
Mass Dependent

<div>Mass-dependent diagonal Born-Oppenheimer corrections (DBOC) to the ab initio electronic ground state potential energy surface for tseveral isotopologues of the ozone molecule are reported for the first time. The comparison with experimental band centers shows a significant improvement of the accuracy with respect to the best Born-Oppenheimer (BO) ab initio calculations reducing the total root-mean-squares (calculated - observed) deviations by about factor of two. For the set of 16O3 vibrations up to five bending and four stretching quanta, the mean (calculated - observed) deviations drop down from 0.7 cm-1 (BO) to about 0.1 cm-1, with the most pronounced improvement seen for bending states and for mixed bend-stretch polyads. In case of bending band centers directly observed under high spectral resolutions, the errors are reduced by more than order of magnitude from observed levels, approaching nearly experimental accuracy. New sets of ab initio vibrational states can be used for improving spectroscopic effective models for analyses of observed high-resolution spectra, particularly in cases of accidental resonances with ,,dark'' states requiring accurate theoretical predictions.</div>

scholarly journals Diagonal Born-Oppenheimer Corrections to the Ground Electronic State Potential Energy Surfaces of Ozone: Improvement of Ab Initio Vibrational Band Centers for the 16O3, 17O3 and 18O3 Isotopologues

2020 ◽  
Author(s):  
Attila Tajti ◽  
Péter Szalay ◽  
Roman V. Kochanov ◽  
Vladimir G. Tyuterev
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Potential Energy Surfaces ◽  
Vibrational States ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
State Potential ◽  
Effective Models ◽  
Energy Surfaces ◽  
Mass Dependent

<div>Mass-dependent diagonal Born-Oppenheimer corrections (DBOC) to the ab initio electronic ground state potential energy surface for tseveral isotopologues of the ozone molecule are reported for the first time. The comparison with experimental band centers shows a significant improvement of the accuracy with respect to the best Born-Oppenheimer (BO) ab initio calculations reducing the total root-mean-squares (calculated - observed) deviations by about factor of two. For the set of 16O3 vibrations up to five bending and four stretching quanta, the mean (calculated - observed) deviations drop down from 0.7 cm-1 (BO) to about 0.1 cm-1, with the most pronounced improvement seen for bending states and for mixed bend-stretch polyads. In case of bending band centers directly observed under high spectral resolutions, the errors are reduced by more than order of magnitude from observed levels, approaching nearly experimental accuracy. New sets of ab initio vibrational states can be used for improving spectroscopic effective models for analyses of observed high-resolution spectra, particularly in cases of accidental resonances with ,,dark'' states requiring accurate theoretical predictions.</div>

Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

2019 ◽  
Author(s):  
Ishita Bhattacharjee ◽  
Debashree Ghosh ◽  
Ankan Paul
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Molecular Orbital ◽  
High Spin ◽  
Potential Energy Surfaces ◽  
Valence Bond ◽  
Deep Minimum ◽  
State Potential ◽  
Energy Surfaces ◽  
Mo Theory

The question of quadruple bonding in C<sub>2</sub> has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C<sub>2</sub>, N<sub>2</sub> and Be<sub>2</sub> and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the<sup> 2S+1</sup>Σ<sub>g/u</sub> (with 2S+1=1,3,5,7,9) states of C<sub>2</sub> and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N<sub>2</sub> and HC≡CH, the presence of a deep minimum in the <sup>7</sup>Σ state of C<sub>2</sub> and CN<sup>+</sup> suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

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