Electronic structure full-potential methods

Now I have introduced a lot of different methods and theories, but how well do they actually work Can they reproduce experimental values, and are they in the same accuracy range as full potential methods Part of these questions were addressed in Paper II for the FCD-EMTO-CPA method, where calculations were performed for magnetic alloys with both compositional and magnetic disorder. This is one of the hardest test one can make for an electronic structure calculation method, and the results are presented in Fig.(6.1)(a) and (b). In Fig.(6.1)(a) are shown calculations of the mixing energy Em x, defined as... 

The possibilities of band structure methods in the studies of the electronic structure and properties of refractory compounds increased greatly with the introduction of the so-called full-potential methods. These methods did not use a spherical approximation for the potential and charge densities in atomic spheres. The obvious drawback of such methods as LMTO, ASW and LAPW is their poor applicability to calculations of anisotropic elastic moduli of crystals (Cu, C44,...). This is also true for cubic refractory compounds. Also quite problematic... 

Jansen H J F and Freeman A J 1984 Total-energy full-potential linearized augmented plane-wave method for bulk solids electronic and structural properties of tungsten Phys. Rev. B 30 561-9... 

Fig. 7. Maps of the electronic charge density in the (110) planes In the ordered twin with (111) APB type displacement. The hatched areas correspond to the charge density higher than 0.03 electrons per cubic Bohr. The charge density differences between two successive contours of the constant charge density are 0.005 electrons per cubic Bohr. Atoms in the two successive (1 10) planes are denoted as Til, All, and T12, A12, respectively, (a) Structure calculated using the Finnis-Sinclair type potential, (b) Structure calculated using the full-potential LMTO method.

In the perfect lattice the dominant feature of the electron distribution is the formation of the covalent, directional bond between Ti atoms produced by the electrons associated with d-orbitals. The concentration of charge between adjacent A1 atoms corresponds to p and py electrons, but these electrons are spatially more dispersed than the d-electrons between titanium atoms. Significantly, there is no indication of a localized charge build-up between adjacent Ti and A1 atoms (Fu and Yoo 1990 Woodward, et al. 1991 Song, et al. 1994). The charge densities in (110) planes are shown in Fig. 7a and b for the structures relaxed using the Finnis-Sinclair type potentials and the full-potential LMTO method, respectively. 

The theoretical description of the electronic structure has been obtained by means of the LAPW method on an ab-initio basis1101. The electronic potential is determined self-consistently for the elementary cell of the bare host structure, which consists of 44 atoms. More complicated systems, where the tubes are filled with water molecules are also taken into account. Recent self-consistent full-potential calculations (FLAPW) are performed to refine the results 11 . 

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