Prediction of possible CaMnO₃modifications using anab initiominimization data-mining approach

Abstract

We have performed a crystal structure prediction study of CaMnO3 focusing on structures generated by octahedral tilting according to group-subgroup relations from the ideal perovskite type (Pm\overline 3 m), which is the aristotype of the experimentally known CaMnO3 compound in the Pnma space group. Furthermore, additional structure candidates have been obtained using data mining. For each of the structure candidates, a local optimization on the ab initio level using density-functional theory (LDA, hybrid B3LYP) and the Hartree--Fock (HF) method was performed, and we find that several of the modifications may be experimentally accessible. In the high-pressure regime, we identify a post-perovskite phase in the CaIrO3 type, not previously observed in CaMnO3. Similarly, calculations at effective negative pressure predict a phase transition from the orthorhombic perovskite to an ilmenite-type (FeTiO3) modification of CaMnO3.

Structural stability of calcium-manganate based CaO(CaMnO3)m (m = 1, 2, 3, ∞) compounds for thermoelectric applications

“…There are contradictory data reported in literature concerning TE [15][16][17][18], bulk [19], and structural [9,12,13,[20][21][22] characteristics of these compounds. For example, it was reported that the absolute values of Seebeck coefficient, S, decrease with increasing temperature for pure CaMnO 3 ; however, bismuth-doped compounds exhibit the opposite trend with a maximum |S|-value equals to 350 µVK -1 at room temperature [15,18].…”

“…For example, the bulk moduli of the pure CaMnO 3 compound (m=∞) reported in literature differ by a factor of four from each other [19]. Importantly, all compounds of the CaO(CaMnO 3 ) m (m=1, 2, 3, ∞) series exhibit contradictory ground state crystal structure data [9,12,13,[20][21][22]. Such ambiguity can obviously make it difficult to analyze experimental and theoretical results, since peculiarities of crystal structures are tightly correlated with electronic and transport properties; this markedly applies for TE materials.…”

Barium Sulfide under Pressure: Discovery of Metastable Polymorphs and Investigation of Electronic Properties on ab Initio Level

“…In the past century, the only possible solution was experimental synthesis. However, in the last few decades, developments in theoretical chemistry and huge improvements in computational power have brought an alternative: theoretical prediction of new compounds and new (meta)­stable crystalline modifications of already existing solids followed by their synthesis. − Recently, many different groups have successfully performed crystal structure prediction using empirical potentials or/and ab initio approach. − In the past few years, we performed such structure predictions, combining global and local optimization routines using empirical, semiempirical, and ab initio potentials, exploring energy landscapes of various binary and ternary systems. − In the present study, as an example system, we chose barium sulfide (BaS), which is, like other barium chalcogenides, a wide band gap semiconductor. , …”

Phase transitions and (p–T–X) behaviour of centrosymmetric perovskites: modelling with transformed crystallographic data

“…The question of the relative stability of alternative perovskite phases has been addressed by several workers employing quantum-mechanical methods (Zagorac et al, 2014) as well as the semi-empirical bond-valence method. Woodward (1997b) initiated this discussion by evaluating the ionic and covalent bonding in perovskites and analysing the conditions of stabilization of favoured tilt systems a À a À c þ , a À a À a À and a 0 a 0 a 0 .…”