It is found to be lower in energy than the 1πu MO, both experimentally and from more sophisticated computational models, so that the expected order of filling is the 3σg before the 1πu. Hence the approximation to ignore the effects of further interactions is valid.
Based on experimental data and advanced computer simulations, the lower energy state is found to be less energetic than the 1πu MO. This finding suggests that the expected order of electron filling should be 3σg before 1πu. Therefore, neglecting the effects of further interactions is justified.