Study of the Structure and Infrared Spectra of LiF, LiCl and LiBr Using Density Functional Theory (DFT)

Abstract

The paper presents a study of the crystal structure of anhydrous halides LiF, LiCl and LiBr using density functional theory. Models composed of 125 atoms were used for this study. The theoretical values of the lattice parameters and the distribution of charges in the crystals were determined. Using the assumed models at the level of theory DFT/B3LYP/6-31+g*, the theoretical infrared spectra of lithium halides (LiF, LiCl and LiBr) were calculated for the first time. Additionally, measurements of experimental far-infrared (FIR) spectra were performed for these salts. All the obtained theoretical values were compared with experimental data obtained by us and those available in the literature.

Innovative Structural Characterization of Natural Villiaumite Crystal

“…Lower intensity bands are also found at the higher wavenumbers in the spectra. Comparing the presented far infrared spectrum of NaF with the spectrum of LiF [44], one can see a shift towards lower frequencies of about 93 cm −1 for the most intense band (for LiF, the most intense band is observed at 353 cm −1 ). This result is consistent with theory, which indicates that the greater the mass of the metal, the more the metal-halogen vibrations shift to lower frequencies [46].…”

“…No imaginary frequencies were determined. In our previous study on LiCl, NaCl, KCl, LiBr and LiF, calculations using a 125-atom model for very similar chemical compounds to those mentioned, gave reliable results [43,44]. The theoretical IR spectrum of the structure of sodium fluoride was derived by representing each band as a Lorentzian-shaped curve.…”

“…We observed the same relationship for a series of chlorides. The most intense bands for LiCl, NaCl and KCl, were observed at 200, 175 and 145 cm −1 , respectively [43,44].…”