1. 
 AlZoubi, Noura, et al.
(författare)

Completeness of the exact muffintin orbitals : application to hydrogenated alloys
 2010

Ingår i: Physical Review B. Condensed Matter and Materials Physics.  10980121. ; 81:4

Tidskriftsartikel (refereegranskat)abstract
 We investigate the basis set convergence of the exact muffintin orbitals by monitoring the equation of state for Al, Cu, and Rh calculated in the conventional facecenteredcubic lattice (strI) and in a facecenteredcubic lattice with one atomic and three empty sites per primitive cell (strII). We demonstrate that three (spd) muffintin orbitals are sufficient to describe Al in both structures, but for strII Cu and Rh at least five (spdfg) orbitals are needed to get converged equilibrium WignerSeitz radius (within <= 0.8%) and bulk modulus (<= 3.3%). We ascribe this slow convergence to the nearly spherical densities localized around the Cu and Rh atoms, which create strongly asymmetric charge distributions within the nearest cells around the empty sites. The potential sphere radius dependence of the theoretical results for structure strII is discussed. It is shown that a properly optimized overlapping muffintin potential in combination with the spdfg basis yields acceptable errors in the equilibrium bulk properties. The basis set convergence is also shown on hydrogenated Sc and Scbased alloys.


2. 
 AlZoubi, Noura, et al.
(författare)

Influence of Magnesium on hydrogenated ScAl1xMgx alloys : a theoretical study
 2011

Ingår i: Computational materials science.  09270256. ; 50:10, s. 28482853

Tidskriftsartikel (refereegranskat)abstract
 Ab initio total energy calculations, based on the projector augmented wave method and the exact mu±ntin orbitals method in combination with the coherentpotential approximation, are used to examine the effect of magnesium on hydrogen absorption/desorption temperature and phase stability of hydrogenated ScAl1xMgx (0 ≤ x ≤ 0:3) alloys. According to the experiments, ScAl1xMgx adopts the CsCl structure, and upon hydrogen absorption it decomposes into ScH2 with CaF2 structure and AlMg with face centered cubic structure. Here we demonstrate that the stability field of the hydrogenated alloys depends sensitively on Mg content and on the microstructure of the decomposed system. For a given microstructure, the critical temperature for hydrogen absorption/desorption increases with Mg concentration.


3. 
 AlZoubi, Noura, et al.
(författare)

Tetragonality of carbondoped ferromagnetic iron alloys : A firstprinciples study
 2012

Ingår i: Physical Review B. Condensed Matter and Materials Physics.  10980121. ; 85:1, s. 014112

Tidskriftsartikel (refereegranskat)abstract
 Using densityfunctional theory in combination with the exact muffintin orbital (EMTO) method and coherent potential approximation, we investigate the alloying effect on the tetragonality of FeC solid solution forming the basis of steels. In order to assess the accuracy of our approach, first we perform a detailed study of the performance of the EMTO method for the Fe(16)C(1) binary system by comparing the EMTO results to those obtained using the projector augmented wave method. In the second step, we introduce different substitutional alloying elements (Al, Cr, Co, Ni) into the Fe matrix and study their impact on the structural parameters. We demonstrate that a small amount of Al, Co, and Ni enhances the tetragonal lattice ratio of Fe(16)C(1) whereas Cr leaves the ratio almost unchanged. The obtained trends are correlated with the singlecrystal elastic parameters calculated for carbonfree alloys.


4. 
 AlZoubi, Noura, et al.
(författare)

The bain path of paramagnetic FeCr based alloys
 2011

Ingår i: Journal of Applied Physics.  00218979. ; 110:1, s. 013708

Tidskriftsartikel (refereegranskat)abstract
 Employing the firstprinciples exact muffintin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic FeCrM (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have nonvanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of FeCr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels.


5. 
 Vitos, Levente, et al.
(författare)

Stainless Steel Alloys from Firstprinciples Theory
 2012

Ingår i: La Metallurgia Italiana.  00260843. ; :5, s. 1927

Tidskriftsartikel (refereegranskat)abstract
 Gaining an accurate description of materials obviously requires the most advanced atomicscale techniques from both experimental and theoretical areas. In spite of the vast number of available techniques, however; the experimental study of the atomicscale properties and phenomena even in simple solids is rather difficult. In steels the challenges become more complex due to the interplay between the structural, chemical and magnetic effects. On the other hand, advanced computational methods based on density functional theory ensure a proper platform for studying the fundamental properties of steel materials from firstprinciples. Our group at the Royal Institute of Technology in Stockholm has an international position in developing and applying computational codes for such applications. Using our ab initio tools, we have presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we review the most important developments within the ab initio quantummechanicsaided steel design with special emphasis on the role of magnetism on the fundamental properties of alloy steels.


6. 
 Zhang, Hualei, et al.
(författare)

Alloying effects on the elastic parameters of ferromagnetic and paramagnetic Fe from firstprinciples theory
 2011

Ingår i: Journal of Applied Physics.  00218979. ; 110:7, s. 073707

Tidskriftsartikel (refereegranskat)abstract
 The elastic properties of paramagnetic facecenteredcubic (fcc) Fe(1x)M(x) (M = Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) random alloys are investigated using the exact muffintin orbitals density functional method in combination with the coherentpotential approximation. We find that the theoretical lattice parameter of fcc Fe is strongly enlarged by Al, V, and Rh and slightly reduced by Si, Cr, and Co, while it remains nearly constant with Mn and Ni. Both positive and negative alloying effects appear for the elastic constants C(ij)(x) of fcc Fe. These findings are in contrast to those obtained for ferromagnetic bodycenteredcubic (bcc) Fe alloys, where all alloying elements considered here are predicted to enlarge the lattice parameter and decrease the C(11)(x) and C(12)(x) elastic constants of bcc Fe. With some exceptions, alloying has much larger effects on ferromagnetic bcc alloys than on paramagnetic fcc ones. Based on the theoretical elastic parameters of the paramagnetic fcc and ferromagnetic bcc phases, simple parameterizations in terms of chemical composition of the equilibrium lattice constants, singlecrystal elastic constants, and polycrystalline elastic moduli of Febased alloys are presented.


7. 
 AlZoubi, Noura, et al.
(författare)

Influence of manganese on the bulk properties of FeCrMn alloys : a firstprinciples study
 2014

Ingår i: Physica Scripta.  00318949. ; 89:12, s. 125702

Tidskriftsartikel (refereegranskat)abstract
 We investigate the effect of manganese on lattice stability and magnetic moments of paramagnetic FeCrMn steel alloys along the Bain path connecting the bodycentered cubic (bcc) and facecentered cubic (fcc) structures. The calculations are carried out using the ab initio exact muffintin orbital method, in combination with the coherent potential approximation, and the paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all FeCrMn alloys considered here, the local magnetic moments on Fe atoms have the minimum values for the fcc structure and the maximum values for the bcc structure, whereas the local magnetic moments on Mn have almost the same value along the constantvolume Bain path. Our results show that Mn addition to paramagnetic FeCr solid solution stabilizes the bcc structure. However, when considering the paramagnetic fcc phase relative to the ferromagnetic bcc ground state, then Mn turns out to be a clear fcc stabilizer, in line with observations.


8. 
 Vitos, Levente, et al.
(författare)

Mechanical properties and magnetism: stainless steel alloys from firstprinciples theory
 2011

Ingår i: 2010 MRS Fall Meeting.  9781618395092 ; s. 6879

Konferensbidrag (refereegranskat)abstract
 Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest subcategory of stainless steels having as the main building blocks the paramagnetic substitutional disordered FeCrNibased alloys. Because of that, austenitic steels represent the primary choice for nonmagnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from firstprinciples theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact MuffinTin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Febased alloys.

