First-principles calculations of parameters of electron-vibrational interaction and estimations of Jahn–Teller stabilization energy for Cr3+ ion in elpasolites

Detailed microscopic study of the crystal field strength 10Dq, constants of electron-vibrational interaction and Huang–Rhys factors for Cs2NaYX6:Cr3+ (X = F, Cl, Br) crystals is presented. The method used in the calculations is the first-principles fully relativistic discrete-variational Dirac–Slater (DV–DS) method based on solving Dirac equations with the local density approximation. The basic features of the method are: (1) the first-principles method without any phenomenological parameters; (2) wide area of applications: to any atom or ion in any symmetry from Oh to C1 for any energy interval from IR to X-ray; (3) possibility to take into account all effects of chemical bond formation. The key idea of the method is that the molecular orbitals (MO) consisting of the wave functions of an impurity ion and ligands are used throughout the calculations rather than atomic wave functions. he calculated values of the Huang–Rhys factors and available in the literature frequencies of normal vibrations for the a1g and eg modes for Cs2NaYX6:Cr3+ (X = F, Cl, Br) crystals the Jahn–Teller stabilization energy for Cr3+ ion in the 4T2g excited state was estimated. The obtained results are compared with estimations from the available experimental data.