  Room-temperature superconductivity has been a long-standing goal for
scientific progress and human development. Thermodynamic stability is a
prerequisite for material synthesis and application. Here, we perform a
combination of high-throughput screening and structural search and uncover two
thermodynamically stable room-temperature superconductors, Fd-3m-Li2NaH17 and
Pm-3n-LiNa3H23, exhibiting extraordinary critical temperature of 340 K at 300
GPa and 310 K at 350 GPa, respectively. Li2NaH17 possesses the highest Tc among
all the thermodynamically stable ternary hydrides hitherto found. The dominated
H density of states at the Fermi level and the strong Fermi surface nesting are
favorable for the emergence of room-temperature superconductivity. Their
excellent superconducting properties help us understand the mechanism of
room-temperature superconductivity and find new room-temperature
superconductors. Interestingly, the structures of LiNa3H23 and Li2NaH17 equal
to the identified type-I and II clathrate geometry. Our results provide a
structural reference and theoretical guidance for later experimental structure
determination and theoretical search for high temperature superconductors.
