By use of molecular-dynamics and simulated annealing technique, we have studied the structural properties of Si_n cluster at zero and high temperature. The results are in good agreement with ab-initio calculations.

A method to calculate the symmetry coefficents in quantum chemistry calculation is in-troduced, which is very useful for calculations of complex cluster. Some results of C₆₀ molecule are aslo represented.

A method of improving the convergence in the DV-_α-SCC calculation are studied in the scheme suggested by Broyden. The obtained result reveals that the convegence of SCC calculations is greatly accelerated by our new calculation procedure. This method may improve the problem of relative slow convergence or even non convegent which are usually happened in the DV-_α-SCC calculations for large cluster with low symmetry.