Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, 8 nanoscale ZnO was recent... more Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, 8 nanoscale ZnO was recently synthesized in the rock salt structure by addition of Mg. Using 9 first-principles methods, we investigated two stabilization routes for accessing rock salt 10 ZnO. The first route is stabilization by Mg addition, which was investigated by considering 11 ZnO−MgO mixed phases. The second route is through size effects, as surface energies 12 become dominant for small nanocrystal sizes. We discovered that the surface energy of 13 rock salt ZnO is surprisingly low at 0.63 J m −2 , which is lower than those of wurtzite and 14 zinc blende ZnO and lower than that of rock salt MgO. We predict that pure ZnO is stable 15 for nanocrystals smaller than 1.6 nm, although Mg additions can greatly extend the size 16 range in which the rock salt phase is stable. Both mixed-phase and core−shell models were 17 considered in the calculations. The present approach could be applied to predict the 18 stabilization of many other nanocrystal phases in deviating crystal structures.
A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion m... more A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is ...
A set of interatomic pair potentials is developed for ZnO based on the Partially Charged Rigid Io... more A set of interatomic pair potentials is developed for ZnO based on the Partially Charged Rigid Ion Model (PCRIM). The derivation of the potentials combines lattice inversion, empirical fitting, and multi-structural ab-initio energy surfaces fitting. We show that, despite the low number of parameters in this model , a wide range of physical properties is accurately reproduced using the new potential model. The calculated lattice parameters and elastic constants of ZnO in the wurtzite (WZ) phase, as well as the lattice parameters and stabilities of ZnO in other high-pressure and metastable phases, agree well with experiment and with density functional theory (DFT) calculations. The calculated transition pressure of the wurtzite-to-rocksalt (WZ-to-RS) transition is 12.3 GPa. A wurtzite-to-honeycomb (WZ-to-HC) phase transition induced by uniaxial pressure along the c axis is simulated by means of molecular dynamics (MD) simulations. The WZ-to-HC transition takes place at an uniaxial pressure of 8.8 GPa while the reverse transition takes place at 2.9 GPa, which is consistent with DFT calculations. Other physical properties, including phonon dispersion and phonon density of states, thermal expansion, melting point, and surface energy calculated using our ZnO potential model are in good agreement with experimental and DFT data. Limitations of the novel ZnO potential model are also discussed. * [email protected] Zinc Oxide (ZnO) is an II-VI group semiconductor with a very wide range of applications, which covers the fields of rubber, ceramic and food industries, paint, pharmaceutics, and electronic devices [1, 2]. The first use of ZnO can be traced back thousands of years ago and elaborate studies on ZnO materials have been carried out for more than seven decades [1, 2]. In recent years, due to the development of the synthesis of low-dimensional ZnO and its potential application in optoelectronic devices [1-6], the interest in ZnO has reached a new peak. In nature, ZnO is stable in the wurtzite (WZ) structure at ambient conditions. Many different methods have been developed to synthesize high-quality bulk and thin-film WZ-ZnO [7-9]. ZnO with the zinc blende (ZB) structure has a relatively higher cohesive energy compared to the WZ structure which is therefore energetically unfavorable at zero temperature and zero pressure conditions [10]. The synthesis of ZB-ZnO can be achieved by growing thin films on specific substrates [11, 12]. A pressure-induced wurtzite-to-rocksalt (WZ-to-RS) phase transition can be observed at a transition pressure of about 10 GPa [13-16]. A further RS-to-CsCl transition was predicted by DFT calculations under at 260 GPa [10], which has not yet been observed in experiments. ZnO nanostructures can be synthesized with diverse morphologies, including nanoparticles and nanorods [17, 18], nanowires and nanobelts [19, 20], nanohelices [21], nanorings and nanotubes [22, 23], nanomultipods and nanoflowers [24-26]. The diversity of the ZnO nanostructures enables the potential application of ZnO materials in transparent electronics, photodetecters, and solar cells, and for nanomotion and biosensing [4-6, 27].
Physical chemistry chemical physics : PCCP, Jan 7, 2015
Knowledge about the intrinsic electronic properties of water is imperative for understanding the ... more Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For si...
Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, 8 nanoscale ZnO was recent... more Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, 8 nanoscale ZnO was recently synthesized in the rock salt structure by addition of Mg. Using 9 first-principles methods, we investigated two stabilization routes for accessing rock salt 10 ZnO. The first route is stabilization by Mg addition, which was investigated by considering 11 ZnO−MgO mixed phases. The second route is through size effects, as surface energies 12 become dominant for small nanocrystal sizes. We discovered that the surface energy of 13 rock salt ZnO is surprisingly low at 0.63 J m −2 , which is lower than those of wurtzite and 14 zinc blende ZnO and lower than that of rock salt MgO. We predict that pure ZnO is stable 15 for nanocrystals smaller than 1.6 nm, although Mg additions can greatly extend the size 16 range in which the rock salt phase is stable. Both mixed-phase and core−shell models were 17 considered in the calculations. The present approach could be applied to predict the 18 stabilization of many other nanocrystal phases in deviating crystal structures.
A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion m... more A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is ...
A set of interatomic pair potentials is developed for ZnO based on the Partially Charged Rigid Io... more A set of interatomic pair potentials is developed for ZnO based on the Partially Charged Rigid Ion Model (PCRIM). The derivation of the potentials combines lattice inversion, empirical fitting, and multi-structural ab-initio energy surfaces fitting. We show that, despite the low number of parameters in this model , a wide range of physical properties is accurately reproduced using the new potential model. The calculated lattice parameters and elastic constants of ZnO in the wurtzite (WZ) phase, as well as the lattice parameters and stabilities of ZnO in other high-pressure and metastable phases, agree well with experiment and with density functional theory (DFT) calculations. The calculated transition pressure of the wurtzite-to-rocksalt (WZ-to-RS) transition is 12.3 GPa. A wurtzite-to-honeycomb (WZ-to-HC) phase transition induced by uniaxial pressure along the c axis is simulated by means of molecular dynamics (MD) simulations. The WZ-to-HC transition takes place at an uniaxial pressure of 8.8 GPa while the reverse transition takes place at 2.9 GPa, which is consistent with DFT calculations. Other physical properties, including phonon dispersion and phonon density of states, thermal expansion, melting point, and surface energy calculated using our ZnO potential model are in good agreement with experimental and DFT data. Limitations of the novel ZnO potential model are also discussed. * [email protected] Zinc Oxide (ZnO) is an II-VI group semiconductor with a very wide range of applications, which covers the fields of rubber, ceramic and food industries, paint, pharmaceutics, and electronic devices [1, 2]. The first use of ZnO can be traced back thousands of years ago and elaborate studies on ZnO materials have been carried out for more than seven decades [1, 2]. In recent years, due to the development of the synthesis of low-dimensional ZnO and its potential application in optoelectronic devices [1-6], the interest in ZnO has reached a new peak. In nature, ZnO is stable in the wurtzite (WZ) structure at ambient conditions. Many different methods have been developed to synthesize high-quality bulk and thin-film WZ-ZnO [7-9]. ZnO with the zinc blende (ZB) structure has a relatively higher cohesive energy compared to the WZ structure which is therefore energetically unfavorable at zero temperature and zero pressure conditions [10]. The synthesis of ZB-ZnO can be achieved by growing thin films on specific substrates [11, 12]. A pressure-induced wurtzite-to-rocksalt (WZ-to-RS) phase transition can be observed at a transition pressure of about 10 GPa [13-16]. A further RS-to-CsCl transition was predicted by DFT calculations under at 260 GPa [10], which has not yet been observed in experiments. ZnO nanostructures can be synthesized with diverse morphologies, including nanoparticles and nanorods [17, 18], nanowires and nanobelts [19, 20], nanohelices [21], nanorings and nanotubes [22, 23], nanomultipods and nanoflowers [24-26]. The diversity of the ZnO nanostructures enables the potential application of ZnO materials in transparent electronics, photodetecters, and solar cells, and for nanomotion and biosensing [4-6, 27].
Physical chemistry chemical physics : PCCP, Jan 7, 2015
Knowledge about the intrinsic electronic properties of water is imperative for understanding the ... more Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For si...
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Papers by Rik Koster