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

S. V. Streltsov, O. A. Popova, D. I. Khomskii

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 effec…