Analytical Potential Energy Function Calculation for Ground State $X^{1}\Sigma^{+}$ of LaCl

The equilibrium geometry, harmonic frequency and dissociation energy of LaCl have been calculated on B3LYP,MP2,QCISD(T) levels with the energy-consistent relativistic effective core potentials approximation. The possible electronic state and reasonable dissociation limit for the ground state of the molecule are determined based on Atomic and Molecular Reaction Statics (AMRS). The Potential energy curve scans for the ground state $X^{1}\\Sigma^{+}$ have been carried out with B3LYP and QCISD(T) methods. Analytical Murrell-Sorbie (M-S) potential energy function and its Dunham expansion form around equilibrium position have also been derived with a nonlinear least-square fit. The calculated spectroscopic constants are in very good agreement with experimental results of vibrotational spectra. The analytical function we got is of much realistic importance due to its use in the calculation of transitional fine structure and the study of reaction dynamic process.