Examining the order-of-limits problem and lattice constant performance of the Tao-Mo functional

Area of Science:

• Condensed matter physics
• Quantum chemistry
• Materials science

Background:

• A semi-local density functional was recently proposed by Tao and Mo.
• This functional is derived from the density matrix expansion of the exchange hole.

Purpose of the Study:

• To critically assess the accuracy and limitations of the Tao-Mo density functional.
• To investigate the impact of the order-of-limits problem on predicted phase transition pressures.
• To re-evaluate the functional's performance in lattice volume predictions.

Main Methods:

• Analysis of the order-of-limits problem in the Tao-Mo functional.
• Comparison of predicted phase transition pressures with experimental and theoretical data.
• Evaluation of lattice volume predictions against reference data, considering anharmonic effects.

Main Results:

• The order-of-limits problem in the Tao-Mo functional leads to severe errors in predicted phase transition pressures.
• The functional's accuracy in predicting lattice volumes is overestimated due to the exclusion of anharmonic zero-point expansion in reference data.
• The claimed superior accuracy of the Tao-Mo functional compared to similar functionals is challenged.

Conclusions:

• The Tao-Mo functional requires significant revision to address the identified order-of-limits issue.
• A more accurate assessment of the functional's performance necessitates the inclusion of anharmonic effects.
• Further research is needed to resolve the order-of-limits problem and improve density functional accuracy.