Programme

P.12 -- Poster, NCTP-39

Date: Tuesday, 29-07-2014

Time: 10h30 - 12h00

Heisenberg antiferromagnetic spin S=1/2 chain Ca2CuO3, a covalent or charge transfer insulator?

Nguyen Thuy Trang(1) and Hoang Nam Nhat (2)

(1) Faculty of Physic, VNU Hanoi University of Science (2) VNU University of Engineering and Technology

Complex cuprate oxide Ca2CuO3, known as a Heisenberg antiferromagnetic (AFM) spin S=1/2 chain compound, has been strongly studied both theoretically and experimently owing to its magnetic low dimensionality which causes various quantum effects such as quantum spin fluctuation, spin-charge separation, strongly reduced charge transfer energy pd. In particular, the strongly reduced pd gives rise to the argument of insulating mechanism in the compound which has not been clarified yet. In this paper, on the base of electronic structure calculations using various ab initio methods, we show the correlation between exchange interaction J, band gap Eg, covalence degree of Cu-O bond and insulating mechanism. Such a correlation clears up the question of the disagreement between previous experimental and theoretical investigations on the insulating mechanism of Ca2CuO3. According to this, we strongly suggest the covalent mechanism for the insulating ground state of the 1 dimension (1D) AFM compound. Due to the strong hybridization between O 2p and Cu 3d states, Hubbard U should be added to both O 2p and Cu 3d shells so that the LDA+U method can reproduce exact band gap, Eg~1.5 eV. Besides, the PBE0 functional, which was believed to be able to well-simulate the exchange interaction within copper oxides, can also predict a good band gap value for the cuprate 1D AFM Ca2CuO3.

Presenter: Nguyen Thuy Trang