398 research outputs found
Analytic continuation-free Green's function approach to correlated electronic structure calculations
We present a new charge self-consistent scheme combining Density Functional
and Dynamical Mean Field Theory, which uses Green's function of multiple
scattering-type. In this implementation the many-body effects are incorporated
into the Kohn-Sham iterative scheme without the need for the numerically
ill-posed analytic continuation of the Green's function and of the self-energy.
This is achieved by producing the Kohn-Sham Hamiltonian in the sub-space of
correlated partial waves and allows to formulate the Green's function directly
on the Matsubara axis. The spectral moments of the Matsubara Green's function
enable us to put together the real space charge density, therefore the charge
self-consistency can be achieved. Our results for the spectral functions
(density of states) and equation of state curves for transition metal elements,
Fe, Ni and FeAl compound agree very well with those of Hamiltonian based
LDA+DMFT implementations. The current implementation improves on numerical
accuracy, requires a minimal effort besides the multiple scattering formulation
and can be generalized in several ways that are interesting for applications to
real materials
Application of the Exact Muffin-Tin Orbitals Theory: the Spherical Cell Approximation
We present a self-consistent electronic structure calculation method based on
the {\it Exact Muffin-Tin Orbitals} (EMTO) Theory developed by O. K. Andersen,
O. Jepsen and G. Krier (in {\it Lectures on Methods of Electronic Structure
Calculations}, Ed. by V. Kumar, O.K. Andersen, A. Mookerjee, Word Scientific,
1994 pp. 63-124) and O. K. Andersen, C. Arcangeli, R. W. Tank, T.
Saha-Dasgupta, G. Krier, O. Jepsen, and I. Dasgupta, (in {\it Mat. Res. Soc.
Symp. Proc.} {\bf 491}, 1998 pp. 3-34). The EMTO Theory can be considered as an
{\it improved screened} KKR (Korringa-Kohn-Rostoker) method which is able to
treat large overlapping potential spheres. Within the present implementation of
the EMTO Theory the one electron equations are solved exactly using the Green's
function formalism, and the Poisson's equation is solved within the {\it
Spherical Cell Approximation} (SCA). To demonstrate the accuracy of the
SCA-EMTO method test calculations have been carried out.Comment: 20 pages, 10 figure
Equation of state and elastic properties of face-centered-cubic FeMg alloy at ultrahigh pressures from first-principles
We have calculated the equation of state and elastic properties of
face-centered cubic Fe and Fe-rich FeMg alloy at ultrahigh pressures from first
principles using the Exact Muffin-Tin Orbitals method. The results show that
adding Mg into Fe influences strongly the equation of state, and cause a large
degree of softening of the elastic constants, even at concentrations as small
as 1-2 at. %. Moreover, the elastic anisotropy increases, and the effect is
higher at higher pressures.Comment: 6 figure
Ab-initio elastic tensor of cubic TiAlN alloy: the dependence of the elastic constants on the size and shape of the supercell model
In this study we discuss the performance of approximate SQS supercell models
in describing the cubic elastic properties of B1 (rocksalt)
TiAlN alloy by using a symmetry based projection technique. We
show on the example of TiAlN alloy, that this projection
technique can be used to align the differently shaped and sized SQS structures
for a comparison in modeling elasticity. Moreover, we focus to accurately
determine the cubic elastic constants and Zener's type elastic anisotropy of
TiAlN. Our best supercell model, that captures accurately both
the randomness and cubic elastic symmetry, results in GPa,
GPa and GPa with 3% of error and for Zener's
elastic anisotropy with 6% of error. In addition, we establish the general
importance of selecting proper approximate SQS supercells with symmetry
arguments to reliably model elasticity of alloys. In general, we suggest the
calculation of nine elastic tensor elements - , , ,
, , , , and , to evaluate and
analyze the performance of SQS supercells in predicting elasticity of cubic
alloys via projecting out the closest cubic approximate of the elastic tensor.
The here described methodology is general enough to be applied in discussing
elasticity of substitutional alloys with any symmetry and at arbitrary
composition.Comment: Submitted to Physical Review
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