  Microscopic formula to describe the entropy of biomolecular solutions are
derived based on the Gibbs formula of entropy, and the generalized Langevin
theory combined with the RISM/3D-RISM theory. Two formula are derived: one is
concerned with the conformational fluctuation of a biomolecule, and the other
with the density fluctuation of solvent around a solute. The formula derived
for the entropy associated with the conformational fluctuation is where N is
the number of atoms in the solute, and A is the determinant of the inverse of
the variance-covariance matrix of conformational fluctuation. The formula for
the entropy of solvent at a pair of positions around a solute is also derived
to be, where n is the number of atoms in a solvent molecule, and B is
essentially the determinant of the matrix of the density-pair-correlation
functions. The entropy at a local position r may be obtained by integrating the
expression by over the entire volume of the system.
  The feasibility of the calculation to find the entropies is discussed.
