  In this paper we propose a tight-binding molecular dynamics with parameters
fitted to first-principles calculations on the smaller clusters and with an
environment correction, to be a powerful technique for studying large
transition/noble metal clusters. In particular, the structure and stability of
$Cu_n$ clusters for $n=3-55$ are studied by using this technique. The results
for small $Cu_n$ clusters ($n=3-9$) show good agreement with {\it ab initio}
calculations and available experimental results. In the size range $10\le n \le
55$ most of the clusters adopt icosahedral structure which can be derived from
the 13-atom icosahedron, the polyicosahedral 19-, 23-, and 26-atom clusters and
the 55-atom icosahedron, by adding or removing atoms. However, a local
geometrical change from icosahedral to decahedral structure is observed for $n
= 40-44$ and return to the icosahedral growth pattern is found at $n=45$ which
continues. Electronic "magic numbers" ($n=2$, 8, 20, 34, 40) in this regime are
correctly reproduced. Due to electron pairing in HOMOs, even-odd alternation is
found. A sudden loss of even-odd alternation in second difference of cluster
binding energy, HOMO-LUMO gap energy and ionization potential is observed in
the region $n\sim40$ due to structural change there. Interplay between
electronic and geometrical structure is found.
