Ab initioapproach to cohesive properties of GdN

Abstract

We apply ab initio quantum-chemical methods to calculate correlation effects on cohesive properties of GdN, thereby extending the recently proposed incremental method to rare-earth compounds. Our calculated values are in reasonable agreement with the experimental cohesive energy ͑86.0%͒ and the experimental lattice constant ͑102.0%͒. Furthermore, we calculate a bulk modulus of 140.3 GPa. Taking into account estimates for the effect of a better basis both at the one-particle level and at the many-particle level, we even reach 98.5% of the experimental cohesive energy and 101.3% of the experimental lattice constant. For this estimate, we obtain a bulk modulus of 163.8 GPa. ͓S0163-1829͑98͒07304-4͔

Cohesive properties of CeN and LaN from first principles

“…I). This value is much lower as the percentage in GdN (63 % [9]), Ce 2 O 3 (71 % [10]), CeO 2 (59 % [12]), and LaN (62% ).…”

“…The data for GdN we have taken from Ref. [9], where the results are obtained for somewhat smaller basis sets, but the incremental scheme was applied with similar truncation criteria as we used. As can be seen from Fig.…”

“…At least two reasons for such result can be found: (i) Neglection of the correlation of the f -shell due to the use of 4f -in-core PP yields some loss in the total correlation energy; (ii) Because of the quite large cluster size better basis set on Ce as well as N can not be employed. In the case of GdN taking into account estimates for the effect of a better basis set both at the one-particle level and at many-particle level, 98.5 % of the experimental cohesive energy has been reached [9]. Comparison of ionic radii of La 3+ (1.172Å), Ce 3+ (1.150Å), and Gd 3+ (1.078Å) shows that the f -shell of Ce with only one electron is not localized as strongly as the f -sell in Gd.…”

“…Dolg et al have developed such pseudopotentials for the all lanthanides [7,8] and yield very good agreement with experimental data for atoms and molecules. The application of these pseudopotentials in solids has started with a correlated treatment of GdN [9]. It was extended on the mean-field level to the series R 2 O 3 (R=La-Pm), where gaussian type basis sets have been optimized for the solid [10].…”

“…Therefore it is desirable to include the correlations with the many-body wavefunction, using so-called quantum-chemical methods for the correlation like coupled cluster. For that reason the method of increments was developed [11] and applied to a wide range of materials including insulating rare-earth compounds like GdN [9] and CeO 2 [12]. We extend these studies while applying the method of increments with a coupled-cluster treatment of the electronic correlations to CeN and LaN.…”