First-Principles Determination of the Ground-State Structure ofLiBH4

Abstract

The potential energy surface of LiBH4 is investigated by a ground-state search method based on simulated annealing and first-principles density functional theory calculations. A new stable orthogonal structure with Pnma symmetry is found, which is 9.66 kJ/mol lower in energy than the proposed Pnma structure by Soulié et al. [J. Alloys Compd. 346, 200 (2002)]. For the high-temperature structure, we suggest a new monoclinic P2/c structure, which is 21.26 kJ/mol over the ground-state energy and shows no lattice instability.

First-principles insight into the degeneracy of ground-state LiBH4structures

“…We find the theoretically predicted Pnma-SA LiBH 4 structure is ∼10 meV/fu higher in energy than the ground state experimental structures (Pnma-XRD and -NPD), strongly contradicting the results in Ref. 10, where this structure is predicted to be ∼100 meV/fu below the experimental XRD structure (Pnma-XRD). Therefore, our results show that the theoretically predicted LiBH 4 structure (Pnma-SA) is not a the lowest-energy DFT structure as described in Ref.…”

“…8-10 is ∼0.2Å. For the XRD determined LiBH 4 structure (Pnma-XRD), our relaxed lattice constants agree well with previous pseudopotential calculations (a=7.34Å, b=4.40Å, c=6.59Å) from Miwa et al 7 and (a=7.25Å, b=4.37Å, c=6.56Å) from Tekin et al 10 For the interatomic distances such as Li-B and B-H (Table I), our DFT relaxed distances of Pnma-NPD and -SA LiBH 4 structures are similar to those in the Refs. 9 and 10, respectively.…”

“…Using the static energies shown in Table II, we find that the experimental structures are indeed the ground state and that the structure obtained from simulated annealing method (SA) is actually higher in energy (not ∼100 meV/fu lower as reported in Ref. 10).…”

“…1-a). In particular, Tekin et al 10 found that their theoretically predicted LiBH 4 ground state structure also has the Pnma space group (we denote the structure as Pnma-SA, Fig. 1-c), and these authors found that their predicted Pnma-SA structure is 9.66 kJ/(mol LiBH 4 ) (or ∼100 meV/fu) lower in energy than the Soulié Pnma-XRD LiBH 4 structure.…”

Ionic conductivity in three crystalline phases of LiBH4under pressure

“…The anomalies observed might be caused by either an isostructural transition of the lattice or a change in the vibrational, librational or rotational dynamics of the molecules (for example a freezing of the molecular rotation [19]), or both. We note that there has been a large theoretical controversy [20][21][22][23][24] regarding the actual structure and stability of phase I, for which most theoretical calculations show that the experimentally observed structure should be unstable and cannot exist. Further theoretical investigations seem to be necessary in order to explain the relationships between structure, stability and transport in this phase.…”