Electronic structure and superconducting properties of lanthanum

Abstract

The total energy and electronic structure of lanthanum have been calculated in the bcc, fcc, hcp, and double hcp structures for pressures up to 35 GPa. The full-potential linearized-augmented-plane-wave method was used with both the local-density approximation ͑LDA͒ and generalized-gradient approximation ͑GGA͒. The correct phase ordering has been found by the GGA results, with lattice parameters and bulk moduli in good agreement with experimental data. The GGA method shows excellent agreement with experiment while the LDA results show some discrepancies. The calculated strain energies for the fcc and bcc structures demonstrate the respective stable and unstable configurations at ambient conditions. The calculated superconductivity properties under pressure for the fcc structure are also found to agree well with measurements. Both LDA and GGA, with minor differences, reproduce well the experimental results for the superconducting critical temperature T c .

Potential high- T c superconducting lanthanum and yttrium hydrides at high pressure

“…We calculated a T c of 6-7 K for fcc La under ambient pressure using μ* = 0.1-0.13, which is close to previous theoretical (46) and experimental work (T c = 6 K) (48), and consistent with high-pressure behavior (T c = 13 K at 20 GPa) (45,48). Likewise, our method gives the T c of elemental Y under pressure to be 15-16 K using μ* = 0.1-0.13, which is also consistent with previous theoretical (15) and experimental studies (T c = 17 K at 89 GPa) (49).…”

Structural, thermodynamic, and mechanical properties of bulk La and A-La2O3

“…It should be pointed out that the present observation that PAW-GGA gives overall better results of bulk La (lattice constants, bulk modulus, cohesive energy, etc.) than PAW-LDA is very similar to theoretical predictions from other approaches such as LMTO and LAPW [51,52].…”

“…After a series of calculations, the derived elastic constants and elastic moduli of bulk La and A-La 2 O 3 are summarized in Table 3. For the sake of comparison, the corresponding calculated and experimental results available in the literature are also listed in Table 3 [38,41,42,52,73,74]. It can be detected from this table that the derived ground-state mechanical properties from the present study are in good agreement with experimental results in the literature [38,41,42,52,73,74].…”

Electronic structure and superconductivity of europium

“…In a previous paper on lanthanum Ref. 13 we were able to accurately determine ground state and superconductivity properties because the unoccupied 4f-bands are localized well above the Fermi level. Calculating similar properties for europium is problematic because common approximations to density functional theory (DFT) such as the local density approximation (LDA) as shown in Fig.…”

“…The hcp N(ǫ) was calculated from Gillan's method 20 as described in Ref. 13 but with a larger Fermi temperature of 0.02 Ry to provide additional weight to the broadening function within the k-point mesh. The sum of the product of energy eigenvalues and matrix elements using 45 k-points in the irreducible Brillouin zone yielded the weighted hcp density of states.…”