We present relativistic effective l-dependent potentials (RELP) for electron — ion Au+. We determined parameters of ELP from Auger and optical spectroscopic data. Orbital energies of atom we calculated by two approaches: non-relativistic with Schr¨odinger equation and relativistic one with Dirac equation. We calculated bound energies of 34 orbital states of Au atom with presently developed effective potential RELP. Results are in good agreement with Dirac— Hartree—Fock calculations and experimental data. We applied potential RELP for oscillator strengths calculations. Our results of oscillator strengths values agree with Dirac—Hartree—Fock these. With the combination of RELP and core polarized dipole correction method we received oscillator strengths conforming to experimental data. We applied the RELP to calculation of the electron-electron screening constant λ in metallic Gold. For these purposes, we calculated the 4f7/2 orbital energy shift of Gold in metallic phase applying perturbation theory with RLEP.