  In this work, we investigate the microstructure of asymptotically flat black
holes with Ruppeiner curvature. Specially, the cosmological constant is
considered to have a fluctuation around 0. Under such consideration, both
repulsive and attractive interactions are found in the Reissner-Nordstr\"om and
Kerr black holes, while the Schwarzschild black hole has dominant attractive
interaction. The result obtained is quite different from that of excluding the
fluctuation of cosmological constant, where these black holes are found to be
always characterised by repulsive interaction.
