Test of dilute gas approximation in quantum mechanical model
  The validity of dilute gas approximation is explored by making use of the large-sized instanton in quantum mechanical model. It is shown that the Euclidean probability amplitude derived through a dilute gas approximation not only cannot explain the result of the linear combination of atomic orbitals approximation, but also does not exhibit a proper limiting case when the size of instanton is very large. 
D.K.Park, Soo-Young Lee, Jae-Rok Kahng, Sahng-Kyoon Yoo, C.H.Lee,   Chang Soo Park and Eui-Soon Yim