Several simple quantum correction factors for classical line shapes, connecting dipole autocorrelation functions to infrared spectra, are compared to exact quantum data in both the frequency and time domain. In addition, the performance of the centroid molecular dynamics approach to line shapes and time-correlation functions is compared to that of these a posteriori correction schemes. The focus is on a tunable model that is able to describe typical hydrogen bonding scenarios covering continuously phenomena from tunneling via low-barrier hydrogen bonds to centered hydrogen bonds with an emphasis on floppy modes and anharmonicities. For these classes of problems, the so-called “harmonic approximation” is found to perform best in most cases, being, however, outperformed by explicit centroid molecular dynamics calculations. In addition, a theoretical analysis of quantum correction factors is carried out within the framework of the fluctuation-dissipation theorem. It can be shown that the harmonic approximation not only restores the detailed balance condition like all other correction factors, but that it is the only one that also satisfies the fluctuation-dissipation theorem. Based on this analysis, it is proposed that quantum corrections of response functions in general should be based on the underlying Kubo-transformed correlation functions.
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1 September 2004
Research Article|
August 18 2004
Quantum corrections to classical time-correlation functions: Hydrogen bonding and anharmonic floppy modes
Rafael Ramı́rez;
Rafael Ramı́rez
Instituto Ciencia de Materiales (CSIC), Campus Cantoblanco, 28049 Madrid, Spain
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Telesforo López-Ciudad;
Telesforo López-Ciudad
Instituto Ciencia de Materiales (CSIC), Campus Cantoblanco, 28049 Madrid, Spain
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Padma Kumar P;
Padma Kumar P
Lehrstuhl für Theoretische Chemie, Ruhr–Universität Bochum, 44780 Bochum, Germany
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Dominik Marx
Dominik Marx
Lehrstuhl für Theoretische Chemie, Ruhr–Universität Bochum, 44780 Bochum, Germany
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J. Chem. Phys. 121, 3973–3983 (2004)
Article history
Received:
March 16 2004
Accepted:
June 01 2004
Citation
Rafael Ramı́rez, Telesforo López-Ciudad, Padma Kumar P, Dominik Marx; Quantum corrections to classical time-correlation functions: Hydrogen bonding and anharmonic floppy modes. J. Chem. Phys. 1 September 2004; 121 (9): 3973–3983. https://doi.org/10.1063/1.1774986
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