BaMnO3 crystallizes in the hexagonal P6_3/mmc space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to three equivalent O(1), three equivalent O(2), and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with nine equivalent Ba(1)O12 cuboctahedra, corners with three equivalent Mn(1)O6 octahedra,  a faceface with one Ba(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Ba(3)O12 cuboctahedra, faces with three equivalent Mn(1)O6 octahedra, and faces with four equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra, corners with six equivalent Mn(2)O6 octahedra, faces with two equivalent Ba(3)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra, and faces with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. In the third Ba site, Ba(3) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(3)O12 cuboctahedra, corners with six equivalent Mn(1)O6 octahedra, faces with two equivalent Ba(2)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra, and faces with six equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Ba(1)O12 cuboctahedra, corners with three equivalent Ba(3)O12 cuboctahedra, faces with three equivalent Ba(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra,  a faceface with one Mn(1)O6 octahedra, and  a faceface with one Mn(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Ba(2)O12 cuboctahedra, corners with three equivalent Mn(2)O6 octahedra, faces with three equivalent Ba(3)O12 cuboctahedra, faces with four equivalent Ba(1)O12 cuboctahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedra are not tilted. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Mn(2) atoms. In the third O site, O(3) is bonded in a distorted L-shaped geometry to one Ba(2), one Ba(3), two equivalent Ba(1), one Mn(1), and one Mn(2) atom.
BaMnO3 crystallizes in the hexagonal P6_3/mmc space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to three equivalent O(1), three equivalent O(2), and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with nine equivalent Ba(1)O12 cuboctahedra, corners with three equivalent Mn(1)O6 octahedra,  a faceface with one Ba(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Ba(3)O12 cuboctahedra, faces with three equivalent Mn(1)O6 octahedra, and faces with four equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. All Ba(1)-O(1) bond lengths are 2.93 Å. All Ba(1)-O(2) bond lengths are 2.94 Å. All Ba(1)-O(3) bond lengths are 2.86 Å. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra, corners with six equivalent Mn(2)O6 octahedra, faces with two equivalent Ba(3)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra, and faces with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. All Ba(2)-O(1) bond lengths are 2.86 Å. All Ba(2)-O(3) bond lengths are 3.06 Å. In the third Ba site, Ba(3) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(3)O12 cuboctahedra, corners with six equivalent Mn(1)O6 octahedra, faces with two equivalent Ba(2)O12 cuboctahedra, faces with six equivalent Ba(1)O12 cuboctahedra, and faces with six equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. All Ba(3)-O(2) bond lengths are 2.85 Å. All Ba(3)-O(3) bond lengths are 2.93 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Ba(1)O12 cuboctahedra, corners with three equivalent Ba(3)O12 cuboctahedra, faces with three equivalent Ba(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra,  a faceface with one Mn(1)O6 octahedra, and  a faceface with one Mn(2)O6 octahedra. All Mn(1)-O(1) bond lengths are 1.91 Å. All Mn(1)-O(3) bond lengths are 1.88 Å. In the second Mn site, Mn(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Ba(2)O12 cuboctahedra, corners with three equivalent Mn(2)O6 octahedra, faces with three equivalent Ba(3)O12 cuboctahedra, faces with four equivalent Ba(1)O12 cuboctahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedra are not tilted. All Mn(2)-O(2) bond lengths are 1.92 Å. All Mn(2)-O(3) bond lengths are 1.93 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Mn(2) atoms. In the third O site, O(3) is bonded in a distorted L-shaped geometry to one Ba(2), one Ba(3), two equivalent Ba(1), one Mn(1), and one Mn(2) atom.