2013 Volume 12 Issue 3 Pages 190-195
Strong basis set dependency of calculated molecular structure of H2− in the ground state 2Σu+ is shown using standard basis sets equipped on Gaussian03: 6-311G**, 6-311++G**, aug-cc-pVTZ, cc-pVTZ, D95, D95++. Calculation methods are HF, MP2 and Full CI. The bond lengths of H2− calculated using standard basis sets without diffuse function are almost twice as long as those of H2 because excess electron occupies anti-bonding orbital of H2. The bond lengths of H2− using standard basis sets with a diffuse function are almost the same as those of H2 because excess electron occupies anti-bonding but very diffuse orbital. The relation between the bond length and ζ of diffuse function is also demonstrated. When ζ is large: the expectation value <r> is small, the bond length of H2− is large. When ζ is small: the expectation value <r> is large, the bond length of H2− is close to that of H2.