Relativistic quantum average-atom model with relativistic exchange potential

We present a relativistic quantum average-atom model where bound and free electrons are treated self-consistently. We propose a relativistic exchange potential that generalizes the nonrelativistic Kohn-Sham exchange potential. The relativistic exchange potential is considered in detail. We interpolate smoothly between the nonrelativistic and ultrarelativistic limits. We neglect the correlation effect. Numerical examples are given.