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  • 1.
    Bigdeli, Sedigheh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Developing the third generation of Calphad databases: what can ab-initio contribute?2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Developing the third generation of Calphad databases with more physical basis valid within a wider temperature range is the aim of the present work. Atomistic scale (ab-initio) methods, particularly techniques based on DFT theory, are used for modelling dierent phenomena, so as to gauge the capacity for use in Calphad modelling. Several systems are investigated in this work for studying dierent phenomena, such as magnetism and vibration of atoms. In the case of pure elements (unaries), thermodynamic properties of Mn, Al and C are optimized in the whole temperature range by the help of new models. In addition, DFT results and specic characteristics of these elements are also used to develop models for describing magnetic properties and atomic vibrations. With regards to coupling between DFT and Calphad, the EMTO technique is used for determining the magnetic ground state of the metastable hcp phase in Fe and Mn, and the TU-TILD technique is used for modelling solid phases above the melting point. TU-TILD is also used for calculating thermodynamic properties of bcc Mn at nite temperatures. The same phenomena are investigated in higher-order systems, i.e. the binaries Fe-Mn and Mn-C. Thermodynamic properties and phase diagrams of these systems are assessed against experimental data. Moreover, the revised magnetic model is used for modelling magnetic properties in these systems.

    It is shown through this investigation that although the DFT methods are powerful tools for model development and for resolving discrepancies between dierent experimental datasets, they should not be overly-trusted. Caution must be taken when using DFT results, since the approximations and assumptions for computational implementations may cause some errors in the results. Moreover, implementing them into Calphad software as a connected methodology is not currently accessible due to the computational limitations.

    It is concluded that coupling between the DFT and Calphad approaches can currently be achieved by using DFT results as an input in Calphad modelling. This will help to improve them until they can be integrated into the Calphad approach by the progress of computational possibilities.

    One of the advantages of developing the third generation Calphad databases is the possibility of using the 0 K DFT results in Calphad modelling, since the new databases are valid down to 0 K. This has not been possible in the past, and such potential opens a new door to bring more physics into the Calphad approach.

  • 2.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ehtehsami, Hossein
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Chen, Qing
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    New description of metastable hcp phase for unaries Fe and Mn: Coupling between first-principles calculations and CALPHAD modeling2016In: Physica Status Solidi B, ISSN 1521-3951, no 9, p. 1830-1836Article in journal (Refereed)
    Abstract [en]

    The main focus in developing the third generation of CALPHADdatabases is to model thermodynamic properties of materialsby using models which are more physically based andvalid down to 0K. First-principles calculations are helpful tochoose and validate those models. Reliable calculation results,for example, at very low temperatures or on metastable systemsreveal physical facts which might be inaccessible by experiments.Following our earlierwork for modeling thermodynamicproperties of pure elements (i.e., Fe and Mn) in third-generationCALPHAD databases, the (hcp) phase was modeled as ametastable phase in the present work. Although hcp phase isjust observed in these two elements under ultra-high pressure, inthe binary Fe–Mn this phase is metastable at ambient temperaturesand pressures. Therefore, it should be properly modeled inunaries for later optimization of binary systems. Based on densityfunctional theory (DFT) calculations, the magnetic groundstate and the magnetic properties of -Fe, -Mn, and their binarysolution phase were calculated. It was found that -Fe is antiferromagnetic(type II) while -Mn has a paramagnetic groundstate. Accordingly, magnetic contributions to thermodynamicproperties were accurately modeled. Moreover, by means ofthe extrapolation of experimental data for the thermodynamicproperties of binary systems and high-pressure data for unaries,the metastable hcp phases at ambient pressure were modeledfor the third-generation CALPHAD database, consistently withother stable phases in the elements Fe and Mn.

  • 3.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Korbmacher, Dominique
    Grabowski, Blazej
    Körmann, Fritz
    Duff, Andrew Ian
    Blomqvist, Andreas
    Neugebauer, Jörg
    DFT based calculations of thermodynamic properties for paramagnetic bcc-Mn at high temperaturesManuscript (preprint) (Other academic)
    Abstract [en]

    In developing the third generation of Calphad databases, density-functional-theory methods are particularly important for validating physical models and for providing input data where experiment is unavailable. Since Cal-phad modelling needs data at finite temperatures additional sampling tech-niques are required, and the recently developed TU-TILD method is one such technique that allows for an efficient and accurate calculation of free energies. It is used in the present work for the complicated paramagnetic bcc phase of Mn. Our results show a good agreement with experimental data, validating that this method is well suited for calculating thermody-namic properties of magnetically complex and dynamically unstable phases as needed for Calphad modelling. It is also shown that a transition from bcc to the ω phase occurs below 1200 K.

  • 4.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    On the third-generation Calphad databases: An updated description of Mn2015In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 10, p. 2199-2208Article in journal (Refereed)
    Abstract [en]

    Aiming for better extrapolations and predictabilities of thermodynamic properties of materials, new thermodynamic models are implemented in the third-generation Calphad databases. In these models, each term contributing to the Gibbs energy has an explicit physical meaning. Furthermore, descriptions of thermodynamic properties of materials are valid from 0K up to high temperatures far above the melting point. As a starting point for the development of large self-consistent third-generation database, the new models in the present work are applied to the unary manganese system. Taking into account both the calculated first principles results and experimental data, thermodynamic model parameters are evaluated. Thermodynamic properties predicted using this description, agree very well with available data. The calculated properties vary smoothly in the whole temperature range, which is another important improvement compared to the second-generation databases.

  • 5.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Qing, Chen
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    A new description for pure C; in developing the third generation of Calphad databases.In: Journal of Phase Equilibria and DiffusionArticle in journal (Other academic)
    Abstract [en]

    In connection to developing the third generation of Calphad databases a new thermodynamic description is presented for unary carbon. Models used in this work have more physical basis and are valid down to 0 K. The anisotropy in graphite, caused by weak Van der Waals inter-plane forces makes it difficult to fit the heat capacity data by a single Einstein tempera-ture for modelling the harmonic vibration of the atoms. By using multiple Einstein temperatures this problem is solved and a good agreement with the experimental data at low temperatures is achieved. Diamond is mod-eled using new models too, and the two-state model is used for modelling the liquid phase.

  • 6.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A thermodynamic assessment of the binary Fe-Mn system for the third generation of Calphad databases2017Manuscript (preprint) (Other academic)
    Abstract [en]

    In developing the third generation of Calphad databases, after having proper models for the unaries, the next step is to assess higher-order systems, i.e. binaries, ternaries etc. A new description for the Fe-Mn system is presented in this work, based on the Calphad approach. New models with a stronger physical basis are used to model Gibbs energy of the phases. For this purpose, the revised magnetic model is used to fit the magnetic properties versus the most recent experimental and DFT data. An acceptable magnetic phase diagram is reproduced, which results in a more reasonable fit for the phase diagram and will prevent possible artefacts in higher-order systems. The descriptions are valid down to 0 K, which make them very useful as an input for modelling phase transformations occurring at low temperatures.  

  • 7.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A thermodynamic assessment of the binary Fe-Mn system for the third generation of Calphad databases2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 64, p. 185-195Article in journal (Refereed)
    Abstract [en]

    In developing the third generation of Calphad databases, the next step after proper description of the unaries is to assess higher-order systems, i.e. binaries, ternaries etc. A new description of the Fe-Mn system is presented in this work, based on the Calphad approach. New models with a stronger physical basis are used to model the Gibbs energy of the phases. For this purpose, the revised magnetic model is used to fit the magnetic properties versus the most recent experimental and ab-initio data. An acceptable magnetic phase diagram is reproduced, and a reasonable fit for the phase diagram is achieved which will prevent possible artefacts in higher-order systems. The description is valid down to 0 K, which make it very useful as a starting point for modelling phase transformations occurring at low temperatures.

  • 8.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhu, L. -F
    Glensk, A.
    Grabowski, B.
    Lindahl, B.
    Hickel, T.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    An insight into using DFT data for Calphad modeling of solid phases in the third generation of Calphad databases, a case study for Al2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 65, p. 79-85Article in journal (Refereed)
    Abstract [en]

    In developing the next generation of Calphad databases, new models are used in which each term contributing to the Gibbs energy has a physical meaning. To continue the development, finite temperature density-functional-theory (DFT) results are used in the present work to discuss and suggest the most applicable and physically based model for Calphad assessments of solid phases above the melting point (the breakpoint for modeling the solid phase in previous assessments). These results are applied to investigate the properties of a solid in the superheated temperature region and to replace the melting temperature as the breakpoint with a more physically based temperature, i.e., where the superheated solid collapses into the liquid. The advantages and limitations of such an approach are presented in terms of a new assessment for unary aluminum.

  • 9.
    Bigdeli, Sedigheh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Zhu, Li-Fang
    Glensk, Albert
    Grabowski, Blazej
    Lindahl, Bonnie
    Hickel, Tilmann
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    An insight into using DFT data for Calphad modelling of solid phases in the third generation of Calphad databases, case study for Al2017Manuscript (preprint) (Other academic)
    Abstract [en]

     In developing the next generation of Calphad databases, new models are used in which each term contributing to the Gibbs energy has a physical meaning. Harmonic vibrations of atoms are modelled using the Einstein temperature; anharmonic vibrations, electronic and magnetic contributions to the solid phases are represented by specific terms. The two-state model is used for the liquid phase. To continue the development, a new description for unary aluminum is presented in this work. In particular, finite temperature density-functional-theory (DFT) results are used to discuss and suggest the most applicable and physically based model for Calphad assessments of solid phases above the melting point. 

  • 10.
    Gunasekara, Saman Nimali
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bigdeli, Sedigheh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Chiu, Justin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Martin, Viktoria
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Thermodynamic assessment of binary erythritol-xylitol phase diagram for phase change materials design2018In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 60, p. 29-36Article in journal (Refereed)
    Abstract [en]

    Here, the erythritol-xylitol binary system was thermodynamically optimized based on available experimental phase equilibrium data, to explore compositions suitable as phase change materials (PCMs) for thermal energy storage (TES). A previous experimental study revealed that erythritol-xylitol was a partially isomorphous system with a eutectic. In the thermodynamic evaluation, the CALPHAD method was employed coupling the phase diagram and thermodynamic property information. There, both unary and binary systems’ experimental data were taken into account, and all phases were described using the substitutional solution model. Finally, a self-consistent thermodynamic description for the erythritol-xylitol system was achieved. The calculated eutectic point is at 76.7 °C and 26.8 mol% erythritol, agreeing well with the experimental data. The calculated phase diagram better-verifies the systems’ solidus and the solvus, disclosing the stable phase relations. Based on the Gibbs energy minimization, phase diagrams can be predicted for the binary and higher order systems, provided the component subsystems are thermodynamically assessed beforehand. In conclusion, to move forward beyond e.g. non-isomorphous simple eutectic systems, methods using Gibbs free energy minimization from a fundamental point-of-view such as CALPHAD are essential.

  • 11.
    Gunasekara, Samman Nimali
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bigdeli, Sedigheh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Chiu, Justin NingWei
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Martin, Viktoria
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Thermodynamic Assessment of Binary Erythritol-Xylitol Phase Diagram for Phase Change Materials DesignManuscript (preprint) (Other academic)
    Abstract [en]

    Here, the experimental phase equilibrium data of the erythritol-xylitol system were thermodynamically optimized, to explore compositions suitable as phase change materials (PCMs) for thermal energy storage (TES). A previous experimental study revealed that erythritol-xylitol was a partially isomorphous system with a eutectic. In the thermodynamic evaluation, the CALPHAD method was employed coupling the phase diagram and thermodynamic property information. There, both unary and binary systems’ experimental data were taken into account, and all phases were described using the substitutional solution model. Finally, a self-consistent thermodynamic description for the erythritol-xylitol system was achieved. The calculated eutectic point is at 76.7 °C and 26.8 mol% erythritol, agreeing well with the experimental data. The calculated phase diagram better-verifies the systems’ solidus and the solvus, disclosing the stable phase relations. Based on the Gibbs energy minimization, phase diagrams can be predicted for the binary and higher order systems, provided the component subsystems are thermodynamically assessed beforehand. In conclusion, to move forward beyond e.g. non-isomorphous simple eutectic systems, methods using Gibbs free energy minimization from a fundamental point-of-view such as CALPHAD are essential.

  • 12.
    Li, Zhou
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bigdeli, Sedigheh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Chen, Q.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermodynamic evaluation of pure Co for the third generation of thermodynamic databases2016In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951Article in journal (Refereed)
    Abstract [en]

    An updated thermodynamic description of pure Co was obtained by applying new models for the third generation of Calphad databases. In these models, different contributions to the heat capacity, especially the vibrational part, were treated separately, each with a clear physical meaning. More importantly, the phase stabilities of the various allotropes are now physically well defined. Thus, the derived thermodynamic properties vary more reasonably and smoothly from 0K and up. Calculated thermodynamic properties were compared with experimental data and good agreement was obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 13.
    Omori, Toshihiro
    et al.
    KTH.
    Bigdeli, Sedigheh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    A Generalized Approach Obeying the Third Law of Thermodynamics for the Expression of Lattice Stability and Compound Energy: A Case Study of Unary Aluminum2018In: JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, ISSN 1547-7037, Vol. 39, no 5, p. 519-531Article in journal (Refereed)
    Abstract [en]

    Recently, Hillert and Selleby proposed a simple method for expression of the lattice stability or Gibbs energy of formation that does not violate the third law of thermodynamics. This method describes the derivation of the Gibbs energy function from high temperatures down to 0 K by interpolation, instead of extrapolation from room temperature to 0 K. In the present work, their original method is discussed in terms of determination of the characteristic parameter values. Keeping the essential interpolation character of their method, a generalized approach is presented for expressing the lattice stability through parameter optimizations. This approach retains the zero point entropy of substances and is in line with the development of the third generation CALPHAD databases. Using the Al unary system as a case study, the lattice stabilities of the hcp and bcc phases are investigated. The respective Einstein temperatures are also evaluated. At high temperatures, the present descriptions reproduce the lattice stabilities suggested by SGTE for the existing second generation of databases, with a reasonable accuracy. More importantly, information from ab initio calculations (total energy at 0 K) is also used for this optimization and the present method results in a physically sounder description of thermodynamic properties at lower temperatures down to 0 K. The present approach provides a simple and flexible way to estimate the lattice stabilities, with potential applicability for the Gibbs energy of formation of stoichiometric compounds and the excess energy of solution phases, in accordance with the third law of thermodynamics.

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