= Residual entropy
{title2=$S_0$}
{wiki}
<Residual entropy> is <entropy> remaining in the zero-temperature limit. An equilibrium ground-state degeneracy $g_0$ gives $S_0=k_B\ln g_0$ for the complete system; an extensive <residual entropy> requires a correspondingly large state count. Frozen configurational disorder can also leave an experimentally inferred <residual entropy> when a sample fails to equilibrate. The zero-entropy perfect-crystal form of the <Third law of thermodynamics> assumes a unique, fully ordered equilibrium <ground state>.
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