The IR spectrum of the shifted 3D harmonic potential for the OH molecule. [The same scale for Panels (a) and (b).]
The IR spectrum of the 3D Morse potential for the OH molecule. (a) Comparison of the LSC-IVR spectrum based on the Kubo-transformed dipole-derivative correlation function to that based on the standard version for T = 100 K. (b) Comparison of the LSC-IVR results at different temperatures. (c) Comparison of the classical results at different temperatures.
Schematic representation of the simulation for the Morse potential. Red line illustrates the Morse potential while Blue line shows its harmonic approximation at the minimum of the well. (a) Classical MD trajectories contain no zero-point energy so the regime that the system can reach is controlled by the energy level on the order of k B T. They oscillate around the minimum of the well and predict almost results very close to the harmonic frequency, which are doomed to be blueshifted from the quantum results. (b) Trajectories in the LSC-IVR contain zero-point energy so the region that the system can access is much broader, accounting for the majority of anharmonicity of the potential surface. Because the zero-point energy is much larger than k B T, the LSC-IVR result is insensitive to the change of the temperature.
Normalized dipole-derivative correlation functions for the 3D Morse potential for T = 100 K.
The normalized local normal frequency distribution of liquid water at T = 300 K using the TTM3-F model. (Note ℏβ ∼ 208.5 cm−1.)
Normalized dipole-derivative correlation functions for liquid water at T = 300 K using the TTM3-F model.
Comparison of simulated IR spectra using the TTM3-F model to the experimental results.
Comparison of simulated IR spectra in the librational regime.
Peak positions of the O–H stretching mode at different temperatures.
Peak positions of the O–H stretching mode estimated by different periods of the LSC-IVR correlation function (same for 100 K and 300 K).
Peak positions of the O–H stretching mode estimated with the Gaussian damping function with different t half parameters (same for 100 K and 300 K).
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