Kinetic temperature vs frequency of the principal modes for the pyrene molecule simulated at 300 K using classical and quantum MD methods.
Kinetic temperature vs frequency of the principal modes, for the naphthalene and coronene molecules simulated at 300 K using classical molecular dynamics. The inset shows the distribution of global kinetic temperature from the 100 trajectories for the pyrene molecule at 300 K, simulated using quantum (ring-polymer) MD and classical MD.
Anharmonic frequency obtained from the principal mode analyses of classical and quantum MD trajectories using the virial estimation, as a function of the harmonic frequency. The insets highlight the correlation between the anharmonic frequencies obtained using the virial formula [Eq. (8)] and the ratio between the eigenvalues of the position and velocity fluctuation matrices [Eq. (10)]. (a) Naphthalene at 300 K with classical MD. (b) Naphthalene at 300 K with quantum MD. (c) Pyrene at 500 K with classical MD. (d) Coronene at 1000 K with quantum MD. In panels [(b) and (d)], the sets of frequencies obtained from centroid MD and ring-polymer MD are shown.
Infrared spectra obtained from Fourier transform of the dipole moment autocorrelation function in classical or quantum molecular dynamics simulations (upper halves, continuous black curves) against spectra reconstructed from the principal mode analysis (lower halves, red histograms). (a) Naphthalene simulated at 500 K from classical MD. (b) Pyrene simulated at 300 K from ring-polymer MD. (c) Coronene simulated at 1000 K from centroid MD.
Vibrational frequencies predicted by the SCP method for the pyrene molecule at different temperatures and in different spectral ranges, assuming quantum or classical statistics, during the iteration procedure. The frequencies are ordered by different colors.
Infrared absorption spectra of the naphthalene molecule obtained from Fourier transformation of the dipole moment autocorrelation function (upper halves, continuous curves) against discrete spectra calculated using the self-consistent phonon approximation (lower halves, histograms). The spectral regions considered are (left panels) and (right panels).
Typical infrared absorption spectra obtained from Fourier transformation of the dipole moment autocorrelation function (upper halves, continuous curves) against discrete spectra calculated using the self-consistent phonon approximation (lower halves, histograms). (a) Pyrene molecule, classical MD in the spectral range of . (b) Coronene molecule, centroid MD in the spectral range of .
Spectrum of anharmonic frequencies obtained for the pyrene molecule using the self-consistent phonon approximation in the classical and quantum mechanical regimes, in the 0–1000 K temperature range. The two uppermost panels highlight the tightest C–H stretching modes, with the black curve resulting from weighting all corresponding modes with their IR intensity. The lower panel emphasizes the spectral range where some frequencies start exhibiting a blueshift with increasing temperature, as indicated by the corresponding colors.
Line shift of selected bands obtained from classical and quantum MD, or predicted by the self-consistent phonons method, as a function of temperature. [(a) and (b)] Naphthalene in two spectral regions. (c) Coronene in the range.
Projection of anharmonic eigenvectors on the harmonic eigenbasis, for the pyrene molecule at 300 K. All modes are sorted according to increasing frequency. The left panels are the results of the principal mode analysis on (a) classical and (c) centroid MD simulations, and the right panels are the results of the self-consistent phonon approximation assuming (b) classical or (d) quantum statistics.
Selected power spectra of the velocity autocorrelation function projected onto selected modes, for the pyrene molecule at 300 K. The numbers in parentheses are the corresponding virial frequencies. (a) Classical MD; (b) centroid MD; and (c) ring-polymer MD.
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