Temperature dependence of the vibrational spectrum of porphycene: a qualitative failure of classical-nuclei molecular dynamics

Abstract

Approximate quantum dynamics succeed in predicting a temperature-dependent blue-shift of the high-frequency stretch bands that arise from vibrational coupling between low-frequency thermally activated modes and high-frequency quantized ones. Classical nuclei molecular dynamics fail and instead predict a red-shift.

Gaussian Process Regression for Materials and Molecules

“…The theoretical calculation of light scattering also requires tensor properties; for example, second-harmonic scattering (SHS) is determined by the first hyperpolarizability tensor, β . 83 , 396 This strategy has been applied to the IR and Raman spectra of molecules 84 and condensed phases 86 , 203 , 394 and even to incorporate the effects of the quantum-mechanical behavior of light nuclei on the spectroscopic properties of complex molecules and condensed phases 85 , 397 —a remarkable feat that would have been all but impossible without ML models that are capable to accurately reproduce all of the properties that are accessible to electronic-structure calculations.…”

Anharmonicity measure for materials

“…This is justified in the investigated temperature range above 300 K for the inorganic solids discussed here. A generalization to a full quantum treatment of the nuclei [21] is possible and could be used to investigate anharmonic effects in organic materials [22], but would go beyond the scope of this work. As mentioned in the Introduction, the harmonic approximation replaces the many-body potential V (R) by a secondorder Taylor expansion around equilibrium R 0 , V (2)…”

Influence of local microenvironment on the double hydrogen transfer in porphycene

“…Observation of this effect was possible because vibrational frequencies directly measured in these works were sensitive to delocalization of the hydrogen wavefunction between the two potential minima. Such an effect should be expected also in the case of porphycene 24 , but anisotropy measurements applied in porphycene studies are sensitive only to hydrogen jumps (localization of the wavefunction in one of the minima). Thus, the situation is simplified and the effects seen by the Raman spectroscopy of terephthalic acid are not observed in time-resolved studies of Pc tautomerization.…”

“…It has been pointed out that better understanding of tunnelling in proton or hydrogen transfer reactions may create a chance for innovations such as an efficient control of the reactions' course 15 , artificial (more efficient) enzymes 16 or fast charging lithium-ion batteries 17 . Therefore, a constant effort is put into development of more accurate models that can be used to describe proton and hydrogen transfer reactions 7,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . Consequently, the experimental data that can be used to verify new models can be invaluable.…”

“…The double hydrogen transfer in porphycene and its derivatives has been extensively studied both theoretically 24,25,27,30,[34][35][36][37] and experimentally. In the latter case the range of phases in which the dynamics of tautomerization was studied includes crystals [38][39][40][41] , solutions [42][43][44][45][46] and single Fig.…”