On Quantum Chemical ab Initio Method and Precision Evaluation of the Calculation Results by Gaussian98 Program

Key words: 
• （ab initio method /
• Gaussian98 /
• single point energy /
• geometry optimization）

Abstract: The structure geometry and single point energy of small molecule are calculated by HF, MP2 and G2 methods and all base sets （except cc-pVQZ）available in Gaussian98 program software package. All these results are compared with the experimental data. It indicates that the molecule geometries optimized by G2 method in Gaussian98 are always in good accordance with experimental results, but the single point energy calculated by MP2 or G2 method differs some much from the experimental data. It is unsuitable to calculate the heat of formation through the single point energy of reactant calculated by methods and base sets provided by Gaussian98.