Infrared absorption spectra of liquid water and deuterated water by Car-Parrinello molecular dynamics

Infrared (IR) absorption spectra plays a key role in the study of thermodynamic and dynamic properties of liquid water. Car-Parrinello molecular dynamics simulations within the framework of density-functional theory are used to study the IR absorption, dielectric function and optical properties of liquid water and deuterated water. Using the energy minimization model to obtain the input structure, we calculate the molecular dipole moment of water and deuterated water at ambient temperature, and then obtain the IR absorption spectra by Fourier transforming the autocorrelated function of dipole moment. As the numerical analysis indicates, the calculated results fit well with previous literature experiments. The absorption peak represents the stretching mode of oxygen-hydrogen covalent bond and shows a slight red shift. The dielectric functions and optical constants of water and deuterated water at the temperature of 303 K are extracted from IR absorption spectrum.