  We calculate angle-dependent heat capacity in a low magnetic field range on
the basis of Kramer-Pesch approximation together with an electronic structure
obtained by first-principles calculations to determine a superconducting gap
function of (TMTSF)2ClO4 through its comparisons with experiments. The present
comparative studies reveal that a nodal d-wave gap function consistently
explains the experimental results for (TMTSF)2ClO4. Especially, it is
emphasized that the observed unusual axis-asymmetry of the angle-dependence
eliminates the possibility of s-wave and node-less d-wave functions. It is also
found that the directional ordering of ClO4 anions does not have any
significant effects on the Fermi surface structure contrary to the previous
modelings since the two Fermi surfaces obtained by the band calculations almost
cross within the present full accuracy in first-principles calculations.
