Figure 4. The plot shows the total energy (in Hartree) of helium atom and the methods used to calculate the values (from left to right, each point corresponds to UHF/STO-3G, UHF/STO-6G, UHF/4-31G**, UHF/6-311++G**, UMP2/6-311G**, UMP4/6-311++G**, UQCISD(TQ)/6-311++G** and Full CI (equivalent to experimental)). The yellow line is a trend line

From

Modeling of Ionization Energy of Elements Using Hartree-Fock Method: An Introduction to Computational Quantum Chemistry for Undergraduate Students

Krishnamohan G P, Thomas Mathew, Simi Saju, James T. Joseph

World Journal of Chemical Education. 2017, 5(3), 112-119 doi:10.12691/wjce-5-3-6