Phase stability of Fe from first principles: Atomistic spin dynamics coupled with 
<i>ab initio</i>
 molecular dynamics simulations and thermodynamic integration

Gambino, Davide; Klarbring, Johan; Alling, Björn

doi:10.1103/physrevb.107.014102

Cited by 4 publications

(3 citation statements)

References 51 publications

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“…All MD studies of bcc phase stability report extremely close free energies of bcc and hcp phases. Recently, it was demonstrated [44] that accounting for spin dynamics is critical for the correct calculation of the temperature of the fcc-bcc transition at P = 1 bar. Such an account might considerably affect the properties of the bcc phase at high P-T conditions of planetary cores, along with a comparably minor impact on the properties of hcp [45].…”

Section: Discussionmentioning

confidence: 99%

A Comparison of Experimental and Ab Initio Structural Data on Fe under Extreme Conditions

Belonoshko

Smirnov

2023

Metals

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Iron is the major element of the Earth’s core and the cores of Earth-like exoplanets. The crystal structure of iron, the major component of the Earth’s solid inner core (IC), is unknown under the high pressures (P) (3.3–3.6 Mbar) and temperatures (T) (5000–7000 K) and conditions of the IC and exoplanetary cores. Experimental and theoretical data on the phase diagram of iron at these extreme PT conditions are contradictory. Though some of the large-scale ab initio molecular dynamics (AIMD) simulations point to the stability of the body-centered cubic (bcc) phase, the latest experimental data are often interpreted as evidence for the stability of the hexagonal close-packed (hcp) phase. Applying large-scale AIMD, we computed the properties of iron phases at the experimental pressures and temperatures reported in the experimental papers. The use of large-scale AIMD is critical since the use of small bcc computational cells (less than approximately 1000 atoms) leads to the collapse of the bcc structure. Large-scale AIMD allowed us to compare the measured and computed coordination numbers as well as the measured and computed structural factors. This comparison, in turn, allowed us to suggest that the computed density, coordination number, and structural factors of the bcc phase are in agreement with those observed in experiments, which were previously assigned either to the liquid or hcp phase.

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Section: Discussionmentioning

confidence: 99%

A Comparison of Experimental and Ab Initio Structural Data on Fe under Extreme Conditions

Belonoshko

Smirnov

2023

Metals

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“…The smaller value of T C obtained in the latter case can be attributed to a decrease of the average local magnetic moment magnitude with temperature, which was reported in previous studies 34,50 . The underestimation in comparison with the experimental value of 1043 K is likely related to neglect of thermal expansion, as all simulations were performed at volume corresponding to the FM bcc phase at 0 K. Apart from the magnetic transition, we also investigated the structural transitions from α to γ (bcc to fcc) and γ to δ (fcc to bcc) phases of Fe using the stress-strain thermodynamic integration method (SSTI) 51,52 (see Methods). In these simulations, it is essential to include the effect of lattice expansion.…”

Section: Phase Transformations At Finite Temperaturesmentioning

confidence: 99%

“…The free energy difference between bcc and fcc, shown in Fig. 9b, was calculated following the application of the SSTI method 51 to magnetic Fe 52 . In this approach, stresses are integrated along a deformation path between the bcc and fcc structures.…”

Section: Md-mc Calculationsmentioning

confidence: 99%

Non-collinear magnetic atomic cluster expansion for iron

Rinaldi,

Mrovec,

Bochkarev

et al. 2024

npj Comput Mater

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The Atomic Cluster Expansion (ACE) provides a formally complete basis for the local atomic environment. ACE is not limited to representing energies as a function of atomic positions and chemical species, but can be generalized to vectorial or tensorial properties and to incorporate further degrees of freedom (DOF). This is crucial for magnetic materials with potential energy surfaces that depend on atomic positions and atomic magnetic moments simultaneously. In this work, we employ the ACE formalism to develop a non-collinear magnetic ACE parametrization for the prototypical magnetic element Fe. The model is trained on a broad range of collinear and non-collinear magnetic structures calculated using spin density functional theory. We demonstrate that the non-collinear magnetic ACE is able to reproduce not only ground state properties of various magnetic phases of Fe but also the magnetic and lattice excitations that are essential for a correct description of finite temperature behavior and properties of crystal defects.

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