To understand the superconductivity and explore the improvement
of transition temperature of H3S, we investigate the effect
of electron or hole injection in H3S with the Im3̅m phase. The results show that the increase
of electron–phonon coupling constant mainly comes from the
softening of phonons when electrons are introduced, while the electron–phonon
coupling strength mainly depends on the change of the electronic density
of states at Fermi level when holes are introduced. We find that the
introduction of holes can improve the transition temperature, and
the increase of hole concentration can further reduce the lowest pressure
point satisfying the stability. In the range of 0.3–0.5 hole
per unit cell, the transition temperature of the charged H3S can be improved to 253 K, which is about 25% larger than the neutral
case (204 K at 200 GPa), and the lowest pressure point satisfying
the stability is reduced to 140 GPa. Combining the hole doping with
the pressure effect, we reveal that the enhancement of transition
temperature is driven by the increase of electronic states at Fermi
level and the softening of phonons. As a result, a novel way is suggested
to further optimize the transition temperature of hydrogen-rich materials.