Coherent Potential Approximation Within the Exact Muffin-Tin Orbitals Theory

Vitos, Levente; Abrikosov, Igor A.; Johansson, Börje

doi:10.1007/0-387-25953-8_25

Cited by 2 publications

(2 citation statements)

References 37 publications

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“…An effective medium is constructed in such a way that it corresponds to a simulated disordered alloy on average, so an atom fills the other atoms as a mean field. This condition is provided by a self-consistent solution of the CPA system of equations [19], [20].…”

Section: Exchange-correlation Functionalmentioning

confidence: 99%

Theoretical description of Ti and Ti alloys from first principles

Skripnyak

2020

Linköping Studies in Science and Technology. Dissertations

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Modern world is known for many advanced technologies and solutions to complex problems. Technical progress runs at high speed. In order to most effectively use materials, given to us by Nature, it is important to know their properties. To do laboratory experiments is often too expensive and time consuming. Therefore, it is very important to possess the knowledge and capabilities of studying materials properties without actual experiments. I use different methods based on the laws of Quantum mechanics to conduct my investigations. In this work I studied from first principles properties of titanium and titanium alloys that are of potential interest for various applications. Titanium was chosen because of its unique properties, which are both useful and reveal interesting physics. First, I investigated elastic properties using density functional theory (DFT) in different implementations, such as the projector augmented wave (PAW) and the exact muffin-tin orbitals (EMTO) methods. The single crystal's elastic constants Cαβ of pure Ti, Ti-V, and Ti-Ni-Al alloys were obtained by calculating the total energy as a function of appropriate strains or stress-strain relations. Disordered substitutional alloys were modeled using a special quasi-random structure (SQS) technique combined with PAW as well as the coherent potential approximation (CPA) combined with EMTO. The concentration dependence of Cαβ and also the family of material characteristics, such as Young's modulus E, bulk modulus B, shear modulus G, Cauchy pressure Pc, Pugh's coefficient k, and Poisson's coefficient ν for the TiV system were estimated and discussed. The elastic properties of alloys in the Ni-Al-Ti system were also calculated and analyzed, as well as the temperaturedependent elastic constants of pure Ti. The influence of the amount of V on iv the mechanical phases stability of body-centered cubic (bcc) Ti-V alloys was studied. It was found that Ti-rich Ti-V alloys are mechanically unstable in the bcc phase, but at higher concentration of V in the system the mechanical stability is increased. It was found that the Ni-Al-Ti system is mechanically stable in accordance with the requirements of mechanical stability for a cubic crystal. The first-principles calculations yielded solution enthalpies for B2 and bcc solid solution alloys. The enthalpies of bcc Ti-V alloys were calculated from first principles at 0 and 1300 K as a function of concentration using static and molecular dynamics simulations. The enthalpy curves for the B2 Ti-V alloys were described as a function of the V concentration by using the calculated solution enthalpies. The enthalpies of the β-phase Ti-V alloys decrease with increasing concentration of vanadium in the range from 0 to 1. Next, selfdiffusion in pure Ti was studied at high temperature using classical and ab initio molecular dynamics. We reveled a physical mechanism entailing a rapid collective movement of numerous (from two to dozens) neighboring titanium atoms along tangled closed-loop paths in defectfree crystal regions. Fur...

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Section: Exchange-correlation Functionalmentioning

confidence: 99%

Theoretical description of Ti and Ti alloys from first principles

Skripnyak

2020

Linköping Studies in Science and Technology. Dissertations

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“…Chemically dis-58 ordered alloys were modelled within the coherent potential approximation 59 (CPA) (Vitos, 2007;Vitos et al, 2005Vitos et al, , 2001. The basis set included s, p, d 60 and f muffin-tin orbitals, and we converged absolute total energy with respect 61 to the number of k-points in the irreducible Brillouin zone to within 0.1 mRy 62 / atom, using 1785 points for fcc and 1184 points for hcp.…”

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confidence: 99%

Configurational thermodynamics of Fe–Ni alloys at Earth's core conditions

Ekholm

Mikhaylushkin

Simak

et al. 2011

Earth and Planetary Science Letters

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By means of ab-initio calculations, we perform an analysis of the configurational thermodynamics, effects of disorder, and structural energy differences in Fe-Ni alloys at the pressure and temperature conditions of the Earth's core. We show from ab-initio calculations that the ordering energies of fccand hcp-structured Fe-Ni solid solutions at these conditions depend sensitively on the alloy configuration, i.e., on the degree of chemical disorder, and are on a scale comparable with the structural energy differences. From configurational thermodynamics simulations we find that a distribution of Fe and Ni atoms in the solutions should be very close to completely disordered at these conditions. Using this model of the Fe-Ni system, we have calculated the fcc-hcp structural free energy difference in a wide pressure-temperature range of 120-360 GPa and 1000-6600 K. Our calculations show that alloying of Fe with Ni below 3000 K favours stabilisation of the fcc phase over the

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Coherent Potential Approximation Within the Exact Muffin-Tin Orbitals Theory

Cited by 2 publications

References 37 publications

Theoretical description of Ti and Ti alloys from first principles

Theoretical description of Ti and Ti alloys from first principles

Configurational thermodynamics of Fe–Ni alloys at Earth's core conditions

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