The Structural, Electronic and Vibrational Properties of <scp>LaCrO</scp>3$$ {}_3 $$. A Quantum Mechanical Investigation by Using an <i>All Electron</i> Gaussian Type Basis Set and a Full Range Hybrid Functional

Abstract

The geometrical, electronic and vibrational properties of LaCrO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msub> </mml:mrow> <mml:annotation>$$ {}_3 $$</mml:annotation></mml:semantics> </mml:math> have been investigated by using an all electron Gaussian type basis set, the B3LYP functional and the CRYSTAL code, and compared with KVF <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msub> </mml:mrow> <mml:annotation>$$ {}_3 $$</mml:annotation></mml:semantics> </mml:math> : in the two compounds the transition metal is formally in d <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msup> </mml:mrow> <mml:annotation>$$ {}^3 $$</mml:annotation></mml:semantics> </mml:math> configuration. The high spin t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msubsup><mml:mrow></mml:mrow> <mml:mrow><mml:mn>2</mml:mn> <mml:mi>g</mml:mi></mml:mrow> <mml:mn>3</mml:mn></mml:msubsup> </mml:mrow> <mml:annotation>$$ {}_{2g}^3 $$</mml:annotation></mml:semantics> </mml:math> ground state excludes the Jahn Teller deformation and the orbital ordering. The energy gain due to the rotation of the octahedra (from the cubic space group Pm <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mn>3</mml:mn> <mml:mo>¯</mml:mo></mml:mover> <mml:mtext>m</mml:mtext></mml:mrow> <mml:annotation>$$ \overline{3}\mathrm{m} $$</mml:annotation></mml:semantics> </mml:math> , N. 221, to space group <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>P</mml:mi> <mml:mfrac><mml:mn>4</mml:mn> <mml:mi>m</mml:mi></mml:mfrac> <mml:mi>bm</mml:mi></mml:mrow> <mml:annotation>$$ P\frac{4}{m} bm $$</mml:annotation></mml:semantics> </mml:math> , N.127, and to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>I</mml:mi> <mml:mfrac><mml:mn>4</mml:mn> <mml:mi>m</mml:mi></mml:mfrac> <mml:mi>cm</mml:mi></mml:mrow> <mml:annotation>$$ I\frac{4}{m} cm $$</mml:annotation></mml:semantics> </mml:math> , N. 140) in the oxide is about 70 times larger than in the fluoride (5.4 vs. 0.08 mE <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mrow></mml:mrow> <mml:mi>h</mml:mi></mml:msub> </mml:mrow> <mml:annotation>$$ {}_h $$</mml:annotation></mml:semantics> </mml:math> ), due to the larger electrostatic forces (a factor four, as the formal charge doubles in going from F^- to O^2-) and the consequently reduced B-X distances. In KVF <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msub> </mml:mrow> <mml:annotation>$$ {}_3 $$</mml:annotation></mml:semantics> </mml:math> , the p states of fluorine are separated by 6.4 eV from the d states of vanadium, whose band is quite narrow (1 eV). In the oxide, on the contrary, the oxygen p states overlap to a large amount with the d states of chromium, whose band is more than 6 eV large. The FM and AFM energy differences, the spin density maps and profiles, and the Mulliken analysis data are also provided for documenting the differences between the oxide and the fluoride.