Shunli Shang - Academia.edu (original) (raw)
Papers by Shunli Shang
Journal of Materials Informatics, 2021
Generative deep learning is powering a wave of new innovations in materials design. In this artic... more Generative deep learning is powering a wave of new innovations in materials design. In this article, we discuss the basic operating principles of these methods and their advantages over rational design through the lens of a case study on refractory highentropy alloys for ultra-high-temperature applications. We present our computational infrastructure and workflow for the inverse design of new alloys powered by these methods. Our preliminary results show that generative models can learn complex relationships in order to generate novelty on demand, making them a valuable tool for materials informatics.
The Nb containing Ni-based superalloys used for the production of large castings are highly sensi... more The Nb containing Ni-based superalloys used for the production of large castings are highly sensible to the formation of macrosegregation defects like freckles and white spots. Production cost can be reduced by better prediction of the freckle formation. The most accepted freckling criterion is the one based on the Rayleigh number, which requires accurate determination of the partition coefficients for the solute elements. In this work, the partition coefficients of Nb and Fe on the ternary system Ni-Fe-Nb were studied by experimental measurements and by thermodynamic calculations. Modified DTA experiments were performed for model alloys, and a thermodynamic database for the Ni-Fe-Nb ternary system was developed. Most of the calculated partition coefficients using the developed model agree well with the experimental data. One exception to this, as will be discussed later, is the partitioning coefficient of Fe for the alloy containing 36 wt. %Fe.
Journal of Materials Chemistry A, 2015
Current advances in first-principles methodology, comprehensive properties, quantitative bonding ... more Current advances in first-principles methodology, comprehensive properties, quantitative bonding and non-polar nature were revealed for α-sulfur and validated by sulfides.
Scientific Reports, 2014
Thermal expansion, defined as the temperature dependence of volume under constant pressure, is a ... more Thermal expansion, defined as the temperature dependence of volume under constant pressure, is a common phenomenon in nature and originates from anharmonic lattice dynamics. However, it has been poorly understood how thermal expansion can show anomalies such as colossal positive, zero, or negative thermal expansion (CPTE, ZTE, or NTE), especially in quantitative terms. Here we show that changes in configurational entropy due to metastable micro(scopic)states can lead to quantitative prediction of these anomalies. We integrate the Maxwell relation, statistic mechanics, and first-principles calculations to demonstrate that when the entropy is increased by pressure, NTE occurs such as in Invar alloy (Fe 3 Pt, for example), silicon, ice, and water, and when the entropy is decreased dramatically by pressure, CPTE is expected such as in anti-Invar cerium, ice and water. Our findings provide a theoretic framework to understand and predict a broad range of anomalies in nature in addition to thermal expansion, which may include gigantic electrocaloric and electromechanical responses, anomalously reduced thermal conductivity, and spin distributions.
The phonon spectra of ␣, , and Ti were studied using the supercell approach. The lattice vibrati... more The phonon spectra of ␣, , and Ti were studied using the supercell approach. The lattice vibrational energy was calculated in the quasiharmonic approximation using both first-principles phonon density of state and Debye model. The thermal electronic contribution to the free energy was evaluated from the integration over the electronic density of states. The Helmholtz energy was thus obtained by combining them with the 0 K total energy calculated within the framework of all-electron projector-augmented-wave method. The thermodynamic properties of ␣ and Ti calculated by phonon and Debye model are very close to each other. The predicted enthalpy, entropy, bulk modulus, thermal expansion coefficient and heat capacity of ␣ are in good agreement with experiments. By comparing with the experimental enthalpy of , we found that the 0 K total energy calculated from bcc Ti is incorrect. This problem can be solved by shifting the total energy of  down by 8 kJ mol −1 to match the experimental value. With the Gibbs energy calculated from the Debye model as a function of pressure and temperature, the phase transformation conditions of ␣ → , ␣ → , and  → were identified. The predicted transition temperature between ␣ and  at ambient pressure and the triple point are close to experiments. It was found that the entropy plays an important role in the → ␣ and ␣ →  transitions, and the thermal electronic contribution to the Gibbs energy cannot be neglected for studying the ␣ →  transition. Our calculations also showed that zero-point energy is crucial to predict the transition pressure of Ti at low temperatures.
Materials Research Letters, 2014
The growth, deformation, and extrinsic faults in binary Mg-X alloys are investigated via first-pr... more The growth, deformation, and extrinsic faults in binary Mg-X alloys are investigated via first-principles calculations. Here, the alloying elements X include Al,
Physical Review B, 2007
Phase stability in ␣and -B has been investigated by using first-principles quasiharmonic phonon ... more Phase stability in ␣and -B has been investigated by using first-principles quasiharmonic phonon calculations. It is found that the defect-free ␣-B is more stable than the defect-free -B at lower temperatures up to the predicted 1388 K. It is revealed that the defect-free -B is mechanically unstable at high temperatures ͑above 1840 K͒, indicated by the appearance of imaginary phonon modes, which can be suppressed by introducing defects, e.g., the extra B atoms. This discovery is consistent with the experimental observations that defects occur commonly in -B.
Physical Review B, 2011
An anomalous energy pathway with energetically-equivalent double saddle points for vacancy mediat... more An anomalous energy pathway with energetically-equivalent double saddle points for vacancy mediated self-diffusion within an hcp-Ti basal plane is unveiled by density functional theory. Examination of migration pathway and phonon force constants suggests that the migrating atom tries to follow the bcc-hcp phase transition via the Burgers shear deformation. We propose that the formed energy local minimum with a bcc-like atomic environment between the two saddle points originates from the existence of high-temperature bcc phase and is a feature of Group IV hcp metals with bcc-hcp phase transition. Computed diffusion coefficients are in favorable accord with experiments for hcp Ti.
Physical Review B, 2010
The longstanding issue of magnetic thermodynamics containing anomalies can be resolved using a re... more The longstanding issue of magnetic thermodynamics containing anomalies can be resolved using a reliable model at finite temperatures: thermodynamic fluctuations among the competing collinear magnetic configurations ͑especially the low energy ones͒ in accordance with canonical partition function. Based on first-principles phonon calculations, we shed light on the magnetic materials ͑as exemplified in bcc Fe͒: the Schottky anomaly of heat capacity and the pressure-dependent Curie temperature stem from the magnetic configurational entropy due to the competition of various magnetic states.
Physica B: Condensed Matter, 2011
The atomic structure and diffusivity in liquid Al 80 Ni 20 are studied by ab initio molecular dyn... more The atomic structure and diffusivity in liquid Al 80 Ni 20 are studied by ab initio molecular dynamics simulations. The local structures are analyzed by the pair correlation function, structure factor, coordinate number, Honneycutt-Anderson bond pair, and Voronoi tessellation methods. It is observed that the amount of icosahedral clusters increases, and the liquid becomes more ordered as the temperature decreases. The predicted self-diffusion coefficients of Al and Ni via the mean square displacements are very close to each other and agree well with the quasi-elastic neutron scattering measurements in the literature. The observation of equal self-diffusivity of Al and Ni is attributed to the formation of local solute-centered polyhedra, coupling the migration of Al and Ni. The Manning dynamic correlation factor is evaluated and found to be close to unity. The predicted interdiffusion coefficients using the Darken equation agree well with experimental data in the literature.
Journal of Physics: Condensed Matter, 2011
In an attempt to obtain reliable first-principles phonon dispersions of random alloys, we have de... more In an attempt to obtain reliable first-principles phonon dispersions of random alloys, we have developed a method to calculate the dynamical matrix, with respect to the wavevector space of the ideal lattice, by averaging over the force constants of a special quasi-random structure. Without additional approximations beyond standard density functional theory, the present scheme takes into account the local atomic position relaxations, the composition disorder, and the force constant disorder in a random alloy. Numerical results are presented for disordered Cu 3 Au, FePd, and NiPd and good agreement between the calculations and the inelastic neutron scattering data is observed.
JOM, 2013
We report our research activities on density functional theory-based alloy thermodynamics, includ... more We report our research activities on density functional theory-based alloy thermodynamics, including method/software developments, the integration of first-principles calculations, CALPHAD modeling, and the automation of phase diagram calculations. Examples to be discussed include phonon dispersions of rhombohedral BiFeO 3 , the solution to the long-outstanding problem of imaginary phonon frequencies for cubic perovskites using EuTiO 3 as an example, the calculation of excess specific heat for the magnetic phase transition in EuTiO 3 , and the automated calculation of a phase diagram for the Al-Mg system.
Journal of Applied Physics, 2012
Due to their high strength and advantageous high-temperature properties, tungsten-based alloys ar... more Due to their high strength and advantageous high-temperature properties, tungsten-based alloys are being considered as plasma-facing candidate materials in fusion devices. Under neutron irradiation, rhenium, which is produced by nuclear transmutation, has been found to precipitate in elongated precipitates forming thermodynamic intermetallic phases at concentrations well below the solubility limit. Recent measurements have shown that Re precipitation can lead to substantial hardening, which may have a detrimental effect on the fracture toughness of W alloys. This puzzle of subsolubility precipitation points to the role played by irradiation induced defects, specifically mixed solute-W interstitials. Here, using first-principles calculations based on density functional theory, we study the energetics of mixed interstitial defects in W-Re, W-V, and W-Ti alloys, as well as the heat of mixing for each substitutional solute. We find that mixed interstitials in all systems are strongly attracted to each other with binding energies of À2.4 to À3:2 eV and form interstitial pairs that are aligned along parallel first-neighbor h111i strings. Low barriers for defect translation and rotation enable defect agglomeration and alignment even at moderate temperatures. We propose that these elongated agglomerates of mixed-interstitials may act as precursors for the formation of needle-shaped intermetallic precipitates. This interstitial-based mechanism is not limited to radiation induced segregation and precipitation in W-Re alloys but is also applicable to other bodycentered cubic alloys.
Journal of Alloys and Compounds, 2014
Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant... more Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant roles in enhancing the mechanical properties of Mg alloys and have been largely investigated separately. In the present work, through detailed investigations of deformation electron density, we show that the electron structures of 10H, 14H, 18R and 24R LPSO structures in Mg originate from those of deformation stacking faults in Mg, and their formation energies can be scaled with respect to formation energy and the number of layers of deformation stacking faults, while the electron structure and formation energy of the 6H LPSO structure are between those of deformation and growth stacking faults. The simulated images of high resolution transmission electron microscopy compare well with experimental observed ones. The understanding of LPSO structures in Mg enables future quantitative investigations of effects of alloying elements on properties of LPSO structures and Mg alloys.
Journal of Alloys and Compounds, 2008
Thermodynamic assessments of the Ca-Ce and Ce-Mg binary systems were carried out by means of the ... more Thermodynamic assessments of the Ca-Ce and Ce-Mg binary systems were carried out by means of the CALPHAD approach complemented by first-principles calculations. The thermodynamic description for the Mg-Ca-Ce system was obtained by combining the derived databases of the Ca-Ce and Ce-Mg systems in the present work with that of the Ca-Mg system from the literature.
Intermetallics, 2009
An energetics database of binary magnesium compounds has been developed from first-principles cal... more An energetics database of binary magnesium compounds has been developed from first-principles calculations. The systems investigated include Mg-X (X ¼ As,
Intermetallics, 2011
b-FeSi 2 and a-FeSi 2. Both the ultrasoft pseudopotential (USPP) and the projector augmented wave... more b-FeSi 2 and a-FeSi 2. Both the ultrasoft pseudopotential (USPP) and the projector augmented wave (PAW) methods are employed to describe the electron-ion interactions. The generalized gradient approximation including PW91 and PBE is employed to describe the exchange-correlation functional. Lattice parameters, bulk modulus, phonon dispersions, and finite temperature thermodynamic properties are calculated and compared with available experimental data, and good agreement is observed. The thermodynamic data obtained in the present work provide better understanding of the stability of binary Fe-Si compounds and can be used for further thermodynamic modeling of this system.
The European Physical Journal B, 2011
Mg2FeH6, which has one of the highest hydrogen storage capacities among Mg based 3d-transitional ... more Mg2FeH6, which has one of the highest hydrogen storage capacities among Mg based 3d-transitional metal hydrides, is considered as an attractive material for hydrogen storage. Within densityfunctional perturbation theory (DFPT), we have investigated the structural, vibrational and thermodynamic properties of Mg2FeH6. The band structure calculation shows that this compound is a semiconductor with a direct X-X energy gap of 1.96 eV. The calculated phonon frequencies for the Raman-active and the infrared-active modes are assigned. The phonon dispersion curves together with the corresponding phonon density of states and longitudinal-transverse optical (LO-TO) splitting are also calculated. Findings are also presented for the temperature-dependent behaviors of some thermodynamic properties such as free energy, internal energy, entropy and heat capacity within the quasi-harmonic approximation based on the calculated phonon density of states.
Computational Materials Science, 2014
The structural and kinetic properties of Ni have been investigated between 300 and 2700 K using a... more The structural and kinetic properties of Ni have been investigated between 300 and 2700 K using ab initio molecular dynamics within the framework of density-functional theory. Equations of state (EOS) are derived from the constant NVT ensembles with N being the number of atoms, V the volume, and T the temperature. From EOS fitting, the equilibrium volumes of Ni are predicted as a function of temperature, which are in good agreement with available experimental data. It is found that the solid-liquid phase transformation can be evaluated by the internal energy change and validated by the appearance of short-range ordering according to structural analysis. Additionally, the diffusion coefficient and shear viscosity are also predicted, in favorable accord with experimental data.
Computational Materials Science, 2009
The effects of alloying elements (Co,
Journal of Materials Informatics, 2021
Generative deep learning is powering a wave of new innovations in materials design. In this artic... more Generative deep learning is powering a wave of new innovations in materials design. In this article, we discuss the basic operating principles of these methods and their advantages over rational design through the lens of a case study on refractory highentropy alloys for ultra-high-temperature applications. We present our computational infrastructure and workflow for the inverse design of new alloys powered by these methods. Our preliminary results show that generative models can learn complex relationships in order to generate novelty on demand, making them a valuable tool for materials informatics.
The Nb containing Ni-based superalloys used for the production of large castings are highly sensi... more The Nb containing Ni-based superalloys used for the production of large castings are highly sensible to the formation of macrosegregation defects like freckles and white spots. Production cost can be reduced by better prediction of the freckle formation. The most accepted freckling criterion is the one based on the Rayleigh number, which requires accurate determination of the partition coefficients for the solute elements. In this work, the partition coefficients of Nb and Fe on the ternary system Ni-Fe-Nb were studied by experimental measurements and by thermodynamic calculations. Modified DTA experiments were performed for model alloys, and a thermodynamic database for the Ni-Fe-Nb ternary system was developed. Most of the calculated partition coefficients using the developed model agree well with the experimental data. One exception to this, as will be discussed later, is the partitioning coefficient of Fe for the alloy containing 36 wt. %Fe.
Journal of Materials Chemistry A, 2015
Current advances in first-principles methodology, comprehensive properties, quantitative bonding ... more Current advances in first-principles methodology, comprehensive properties, quantitative bonding and non-polar nature were revealed for α-sulfur and validated by sulfides.
Scientific Reports, 2014
Thermal expansion, defined as the temperature dependence of volume under constant pressure, is a ... more Thermal expansion, defined as the temperature dependence of volume under constant pressure, is a common phenomenon in nature and originates from anharmonic lattice dynamics. However, it has been poorly understood how thermal expansion can show anomalies such as colossal positive, zero, or negative thermal expansion (CPTE, ZTE, or NTE), especially in quantitative terms. Here we show that changes in configurational entropy due to metastable micro(scopic)states can lead to quantitative prediction of these anomalies. We integrate the Maxwell relation, statistic mechanics, and first-principles calculations to demonstrate that when the entropy is increased by pressure, NTE occurs such as in Invar alloy (Fe 3 Pt, for example), silicon, ice, and water, and when the entropy is decreased dramatically by pressure, CPTE is expected such as in anti-Invar cerium, ice and water. Our findings provide a theoretic framework to understand and predict a broad range of anomalies in nature in addition to thermal expansion, which may include gigantic electrocaloric and electromechanical responses, anomalously reduced thermal conductivity, and spin distributions.
The phonon spectra of ␣, , and Ti were studied using the supercell approach. The lattice vibrati... more The phonon spectra of ␣, , and Ti were studied using the supercell approach. The lattice vibrational energy was calculated in the quasiharmonic approximation using both first-principles phonon density of state and Debye model. The thermal electronic contribution to the free energy was evaluated from the integration over the electronic density of states. The Helmholtz energy was thus obtained by combining them with the 0 K total energy calculated within the framework of all-electron projector-augmented-wave method. The thermodynamic properties of ␣ and Ti calculated by phonon and Debye model are very close to each other. The predicted enthalpy, entropy, bulk modulus, thermal expansion coefficient and heat capacity of ␣ are in good agreement with experiments. By comparing with the experimental enthalpy of , we found that the 0 K total energy calculated from bcc Ti is incorrect. This problem can be solved by shifting the total energy of  down by 8 kJ mol −1 to match the experimental value. With the Gibbs energy calculated from the Debye model as a function of pressure and temperature, the phase transformation conditions of ␣ → , ␣ → , and  → were identified. The predicted transition temperature between ␣ and  at ambient pressure and the triple point are close to experiments. It was found that the entropy plays an important role in the → ␣ and ␣ →  transitions, and the thermal electronic contribution to the Gibbs energy cannot be neglected for studying the ␣ →  transition. Our calculations also showed that zero-point energy is crucial to predict the transition pressure of Ti at low temperatures.
Materials Research Letters, 2014
The growth, deformation, and extrinsic faults in binary Mg-X alloys are investigated via first-pr... more The growth, deformation, and extrinsic faults in binary Mg-X alloys are investigated via first-principles calculations. Here, the alloying elements X include Al,
Physical Review B, 2007
Phase stability in ␣and -B has been investigated by using first-principles quasiharmonic phonon ... more Phase stability in ␣and -B has been investigated by using first-principles quasiharmonic phonon calculations. It is found that the defect-free ␣-B is more stable than the defect-free -B at lower temperatures up to the predicted 1388 K. It is revealed that the defect-free -B is mechanically unstable at high temperatures ͑above 1840 K͒, indicated by the appearance of imaginary phonon modes, which can be suppressed by introducing defects, e.g., the extra B atoms. This discovery is consistent with the experimental observations that defects occur commonly in -B.
Physical Review B, 2011
An anomalous energy pathway with energetically-equivalent double saddle points for vacancy mediat... more An anomalous energy pathway with energetically-equivalent double saddle points for vacancy mediated self-diffusion within an hcp-Ti basal plane is unveiled by density functional theory. Examination of migration pathway and phonon force constants suggests that the migrating atom tries to follow the bcc-hcp phase transition via the Burgers shear deformation. We propose that the formed energy local minimum with a bcc-like atomic environment between the two saddle points originates from the existence of high-temperature bcc phase and is a feature of Group IV hcp metals with bcc-hcp phase transition. Computed diffusion coefficients are in favorable accord with experiments for hcp Ti.
Physical Review B, 2010
The longstanding issue of magnetic thermodynamics containing anomalies can be resolved using a re... more The longstanding issue of magnetic thermodynamics containing anomalies can be resolved using a reliable model at finite temperatures: thermodynamic fluctuations among the competing collinear magnetic configurations ͑especially the low energy ones͒ in accordance with canonical partition function. Based on first-principles phonon calculations, we shed light on the magnetic materials ͑as exemplified in bcc Fe͒: the Schottky anomaly of heat capacity and the pressure-dependent Curie temperature stem from the magnetic configurational entropy due to the competition of various magnetic states.
Physica B: Condensed Matter, 2011
The atomic structure and diffusivity in liquid Al 80 Ni 20 are studied by ab initio molecular dyn... more The atomic structure and diffusivity in liquid Al 80 Ni 20 are studied by ab initio molecular dynamics simulations. The local structures are analyzed by the pair correlation function, structure factor, coordinate number, Honneycutt-Anderson bond pair, and Voronoi tessellation methods. It is observed that the amount of icosahedral clusters increases, and the liquid becomes more ordered as the temperature decreases. The predicted self-diffusion coefficients of Al and Ni via the mean square displacements are very close to each other and agree well with the quasi-elastic neutron scattering measurements in the literature. The observation of equal self-diffusivity of Al and Ni is attributed to the formation of local solute-centered polyhedra, coupling the migration of Al and Ni. The Manning dynamic correlation factor is evaluated and found to be close to unity. The predicted interdiffusion coefficients using the Darken equation agree well with experimental data in the literature.
Journal of Physics: Condensed Matter, 2011
In an attempt to obtain reliable first-principles phonon dispersions of random alloys, we have de... more In an attempt to obtain reliable first-principles phonon dispersions of random alloys, we have developed a method to calculate the dynamical matrix, with respect to the wavevector space of the ideal lattice, by averaging over the force constants of a special quasi-random structure. Without additional approximations beyond standard density functional theory, the present scheme takes into account the local atomic position relaxations, the composition disorder, and the force constant disorder in a random alloy. Numerical results are presented for disordered Cu 3 Au, FePd, and NiPd and good agreement between the calculations and the inelastic neutron scattering data is observed.
JOM, 2013
We report our research activities on density functional theory-based alloy thermodynamics, includ... more We report our research activities on density functional theory-based alloy thermodynamics, including method/software developments, the integration of first-principles calculations, CALPHAD modeling, and the automation of phase diagram calculations. Examples to be discussed include phonon dispersions of rhombohedral BiFeO 3 , the solution to the long-outstanding problem of imaginary phonon frequencies for cubic perovskites using EuTiO 3 as an example, the calculation of excess specific heat for the magnetic phase transition in EuTiO 3 , and the automated calculation of a phase diagram for the Al-Mg system.
Journal of Applied Physics, 2012
Due to their high strength and advantageous high-temperature properties, tungsten-based alloys ar... more Due to their high strength and advantageous high-temperature properties, tungsten-based alloys are being considered as plasma-facing candidate materials in fusion devices. Under neutron irradiation, rhenium, which is produced by nuclear transmutation, has been found to precipitate in elongated precipitates forming thermodynamic intermetallic phases at concentrations well below the solubility limit. Recent measurements have shown that Re precipitation can lead to substantial hardening, which may have a detrimental effect on the fracture toughness of W alloys. This puzzle of subsolubility precipitation points to the role played by irradiation induced defects, specifically mixed solute-W interstitials. Here, using first-principles calculations based on density functional theory, we study the energetics of mixed interstitial defects in W-Re, W-V, and W-Ti alloys, as well as the heat of mixing for each substitutional solute. We find that mixed interstitials in all systems are strongly attracted to each other with binding energies of À2.4 to À3:2 eV and form interstitial pairs that are aligned along parallel first-neighbor h111i strings. Low barriers for defect translation and rotation enable defect agglomeration and alignment even at moderate temperatures. We propose that these elongated agglomerates of mixed-interstitials may act as precursors for the formation of needle-shaped intermetallic precipitates. This interstitial-based mechanism is not limited to radiation induced segregation and precipitation in W-Re alloys but is also applicable to other bodycentered cubic alloys.
Journal of Alloys and Compounds, 2014
Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant... more Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant roles in enhancing the mechanical properties of Mg alloys and have been largely investigated separately. In the present work, through detailed investigations of deformation electron density, we show that the electron structures of 10H, 14H, 18R and 24R LPSO structures in Mg originate from those of deformation stacking faults in Mg, and their formation energies can be scaled with respect to formation energy and the number of layers of deformation stacking faults, while the electron structure and formation energy of the 6H LPSO structure are between those of deformation and growth stacking faults. The simulated images of high resolution transmission electron microscopy compare well with experimental observed ones. The understanding of LPSO structures in Mg enables future quantitative investigations of effects of alloying elements on properties of LPSO structures and Mg alloys.
Journal of Alloys and Compounds, 2008
Thermodynamic assessments of the Ca-Ce and Ce-Mg binary systems were carried out by means of the ... more Thermodynamic assessments of the Ca-Ce and Ce-Mg binary systems were carried out by means of the CALPHAD approach complemented by first-principles calculations. The thermodynamic description for the Mg-Ca-Ce system was obtained by combining the derived databases of the Ca-Ce and Ce-Mg systems in the present work with that of the Ca-Mg system from the literature.
Intermetallics, 2009
An energetics database of binary magnesium compounds has been developed from first-principles cal... more An energetics database of binary magnesium compounds has been developed from first-principles calculations. The systems investigated include Mg-X (X ¼ As,
Intermetallics, 2011
b-FeSi 2 and a-FeSi 2. Both the ultrasoft pseudopotential (USPP) and the projector augmented wave... more b-FeSi 2 and a-FeSi 2. Both the ultrasoft pseudopotential (USPP) and the projector augmented wave (PAW) methods are employed to describe the electron-ion interactions. The generalized gradient approximation including PW91 and PBE is employed to describe the exchange-correlation functional. Lattice parameters, bulk modulus, phonon dispersions, and finite temperature thermodynamic properties are calculated and compared with available experimental data, and good agreement is observed. The thermodynamic data obtained in the present work provide better understanding of the stability of binary Fe-Si compounds and can be used for further thermodynamic modeling of this system.
The European Physical Journal B, 2011
Mg2FeH6, which has one of the highest hydrogen storage capacities among Mg based 3d-transitional ... more Mg2FeH6, which has one of the highest hydrogen storage capacities among Mg based 3d-transitional metal hydrides, is considered as an attractive material for hydrogen storage. Within densityfunctional perturbation theory (DFPT), we have investigated the structural, vibrational and thermodynamic properties of Mg2FeH6. The band structure calculation shows that this compound is a semiconductor with a direct X-X energy gap of 1.96 eV. The calculated phonon frequencies for the Raman-active and the infrared-active modes are assigned. The phonon dispersion curves together with the corresponding phonon density of states and longitudinal-transverse optical (LO-TO) splitting are also calculated. Findings are also presented for the temperature-dependent behaviors of some thermodynamic properties such as free energy, internal energy, entropy and heat capacity within the quasi-harmonic approximation based on the calculated phonon density of states.
Computational Materials Science, 2014
The structural and kinetic properties of Ni have been investigated between 300 and 2700 K using a... more The structural and kinetic properties of Ni have been investigated between 300 and 2700 K using ab initio molecular dynamics within the framework of density-functional theory. Equations of state (EOS) are derived from the constant NVT ensembles with N being the number of atoms, V the volume, and T the temperature. From EOS fitting, the equilibrium volumes of Ni are predicted as a function of temperature, which are in good agreement with available experimental data. It is found that the solid-liquid phase transformation can be evaluated by the internal energy change and validated by the appearance of short-range ordering according to structural analysis. Additionally, the diffusion coefficient and shear viscosity are also predicted, in favorable accord with experimental data.
Computational Materials Science, 2009
The effects of alloying elements (Co,