Figure 1

(a) View down 〈001〉 of the tetragonal structure, the (110) planes are indicated by black lines, (b) view down 〈100〉 M₁ structure, the (011) planes are indicated by black lines, illustrating that they correspond to the same distance as the tetragonal (110) planes, the off-centre positioning of the vanadium atoms in the M₁ structure from the anti-ferroelectric twist is also apparent (c) view down 〈010〉 of the tetragonal structure, the evenly spaced vanadium chains are visible, running parallel to the c-axis and the (101) planes are indicated with black lines, (d) view down 〈010〉 of the M₁ structure, with the Peierls paired vanadium chains visible running parallel to the a-axis and the planes are marked with black lines. These are shifted by one half of a lattice spacing for better comparison to the tetragonal (101) planes, illustrating that both correspond to the same distance, (e) same perspective as (b) but with the “V-V Corner Long”, “V-V Corner Short”, “V-O Apical Long” and “V-O Apical Short” distances marked and (f) same perspective as (d) but with the “V-V Chain Short” and “V-V Chain Long” distances indicated by the letters “S” and “L” respectively.