Comment on ``Sodium Pyroxene NaTiSi$_2$O$_6$: Possible Haldane Spin-1 Chain System''

TL;DR

This study uses the LDA+U method to analyze the magnetic and electronic properties of NaTiSi$_2$O$_6$, confirming Ti-Ti dimer formation and orbital ordering, and highlighting the importance of correlation effects neglected in LSDA calculations.

Contribution

It demonstrates that including correlation effects via LDA+U is crucial for accurately describing NaTiSi$_2$O$_6$'s properties, challenging previous LSDA-based interpretations.

Findings

LDA+U predicts larger band gaps than LSDA.

LDA+U confirms Ti-Ti singlet dimer formation.

Results disagree with earlier LSDA-based studies.

Abstract

Magnetic and electronic properties of NaTiSi$_2$O$_6$ in low temperature phase were studied in the framework of the LDA+U approximation. We stress that neglecting correlation effects in LSDA calculations one obtains not only several times smaller value of the band gap, but also fails to describe magnetic properties of NaTiSi$_2$O$_6$. Our LDA+U results confirm formation of singlet Ti-Ti dimers in low temperature phase of NaTiSi$_2$O$_6$ driven by corresponding orbital ordering [J. Phys. Soc. Jpn. 71, 1423 (2002)], but strongly disagree with the LSDA results and interpretations of Phys. Rev. Lett. 93, 036401 (2004).