, where |E 0 max | denotes the amplitude of external electric field, ω 0 is the excitation frequency, t 0 = 6.60 fs is the center of Gausstype laser and τ = 1.60 fs is the width of laser pulse. When the water molecule is in the proximity of the nanosized Au tetrahedron, the field E(r, t), interacted with Au 20 @H 2 O, includes the incident laser field ⃗ E 0 (t) and the scattered field ⃗ E sca (r, t) generated by the truncated tetrahedron (Au 20 is cut off from this nanosized tetrahedron). This inhomogeneous near field can be expressed as E(r, t) = E s (r)E t (t), where E s (r) is the spatial function that represents the non-uniform distribution of fields and E t (t) is the temporal function which matches the incident laser pulse. In order to describe the non-uniformity of the enhanced near-field, we need to obtain the expression of the spatial function