We present systematic total energy calculations for metals ͑Al, Fe, Ni, Cu, Rh, Pd, and Ag͒ and semiconductors ͑C, Si, Ge, GaAs, InSb, ZnSe, and CdTe͒, based on the all-electron full-potential ͑FP͒ Korringa-KohnRostoker Green's-function method, using density-functional theory. We show that the calculated lattice parameters and bulk moduli are in excellent agreement with calculated results obtained by other FP methods, in particular, the full-potential linear augmented-plane-wave method. We also investigate the difference between the local-spin-density approximation ͑LSDA͒ and the generalized-gradient approximation ͑GGA͒ of Perdew and Wang ͑PW91͒, and find that the GGA corrects the deficiencies of the LSDA for metals, i.e., the underestimation of equilibrium lattice parameters and the overestimation of bulk moduli. On the other hand, for semiconductors the GGA gives no significant improvement over the LSDA. We also discuss that a perturbative GGA treatment based on FP-LSDA spin densities gives very accurate total energies. Further, we demonstrate that the accuracy of structural properties obtained by FP-LSDA and FP-GGA calculations can also be achieved in the calculations with spherical potentials, provided that the full spin densities are calculated and all Coulomb and exchange integrals over the Wigner-Seitz cell, occurring in the double-counting contributions of the total energy, are correctly evaluated. ͓S0163-1829͑99͒15331-1͔

We present first-principles calculations of the lattice relaxations and hyperfine fields of heavy impurities in bcc Fe. We consider impurities of the 5sp and 6sp series, containing the largest atoms in the periodic table.As an application we calculate the hyperfine fields of these impurities and in particular the effects of lattice relaxations on these fields. The calculations are based on a full-potential Korringa-Kohn-Rostoker Green'sfunction method for defects and employ the local spin-density approximation for the exchange and correlation effects. The nonspherical parts of the potential and the charge density are included in the calculations and the forces are calculated by an ionic version of the Hellmann-Feynman theorem. The resulting lattice relaxations are relatively small, even for the largest impurities considered. The comparison of the calculated hyperfine fields with the experimental data shows that the inclusion of lattice relaxations improves the overall agreement with experiment.

The electronic and geometrical structures, in particular the electric field gradients (EFGs), of ͓CdD͔ 2 (D P, As, Sb) acceptor-donor pairs in Si and Ge are studied using the full potential Korringa-KohnRostoker Green's function method. In addition, also neutral complexes (͓CdD͔ 0 ) and trimers (͓CdD 2 ͔ 0 ) in Si are investigated. The EFG depends very sensitively on the large lattice relaxations induced by the defects and can be understood by a simple hybridization model. Our calculations are in good agreement with experimental results and provide a consistent picture of acceptor-donor complexes in Si and Ge. PACS numbers: 71.55.Cn, 61.72.Tt, The donor-acceptor pairs in silicon and germanium have attracted intensive research interest for a long time [1][2][3][4][5]. If impurities with opposite charges are either intentionally or unintentionally introduced in semiconductors, the Coulomb attraction leads to the formation of donoracceptor complexes which can cause serious technological problems such as an uncontrolled annihilation or creation of charge carriers. To study the behavior of these defects, mostly nuclear techniques such as perturbed gg angular correlation (PAC) experiments were successfully applied to obtain microscopic information on an atomic scale. A very popular and well-known probe atom is the radioactive 111 In͞ 111 Cd nucleus. In these experiments initially a dimer complex is formed consisting of the In acceptor and a donor atom such as P, As, or Sb, so that neutral ͓InD͔ 0 (D P, As, Sb) pairs are produced. Since such neutral pairs have no states in the gap and thus are not magnetically or electrically active, very little information can be obtained with other experimental methods. After the decay 111 In ! 111 Cd, the PAC measurement takes place at the daughter complex CdD. The fact that the electric field gradient is independent from the InD mother complex has been proven by PAC experiments starting from the 111m Cd nucleus as mother probe atom [3]. Because of the pair formation the cubic surrounding of the probe atom 111 Cd is disturbed, leading to an electric field gradient (EFG) at the Cd site which can be determined in particular for nonmagnetic systems. This "fingerprint" of the defect system gives some important information about the defect structure. For instance, the main axis of the EFG is found to point along the [111] direction (h 0), which strongly suggests a nearest neighbor (nn) pair configuration. However, for a fundamental understanding of the complexes electronic structure calculations are needed [3], which can be performed with good precision by density-functional methods [6,7]. The use of pseudopotential methods, which usually give excellent results in semiconductor physics, is not suitable in this case since the EFG is determined by the p charge density in the inner core region [6], so that up to now no theoretical treatment of these fundamental acceptor-donor complexes in Si and Ge exists.In this paper we calculate the electronic and geometrical structures and the EFGs of s...

We present a detailed investigation of bulk properties of MgO and lattice relaxations around divalent impurities in MgO by means of the full-potential Korringa-Kohn-Rostoker Green's function method. The local-density approximation and the perturbative generalized gradient corrections are used to calculate the lattice constant and bulk modulus of MgO. We obtain a very good description of the ground properties of MgO. Lattice relaxations around divalent impurities in MgO are determined using an ionic version of the Hellmann-Feynman theorem.

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