However, the energy difference obtained by such an approach will invariably be an overestimate of the true value.The discrepancy arises from a phenomenon known as basis set superposition error (BSSE).

• 很显然，使用较小的和不合适的基组(对离核较远的电子分布不能提供好的描述，特别是在非键相互作用最强的区域)，BSSE会更明显。