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From Bulk to Nano Understanding the Transition through Computer Simulations
Published in Esteban A. Franceschini, Nanostructured Multifunctional Materials Synthesis, Characterization, Applications and Computational Simulation, 2021
On the other hand, sometimes it is convenient to treat valence and core electrons differently. All-electron methods take explicitly into account all the electrons of the system. However, many properties of the materials and the chemistry involved in the reactions are mostly determined by the valence electrons alone, making the computational effort of all-electron approaches sometimes excessive. The pseudopotential method (Phillips and Kleinman 1959) simplifies the atomic description by implementing an effective potential to represent the core electrons and the nuclei, and only the valence electrons, attached to this potential, are explicitly described. Some popular approaches are the norm-conserving (Hamann et al. 1979) and ultrasoft (Vanderbilt 1990) pseudopotentials and the Projector Augmented Waves (PAW) (Kresse and Joubert 1999).
Structural and Electronic Properties of GaSb/InSb and InAs/lnSb Superlattices
Published in M. O. Manasreh, Antimonide-Related Strained-Layer Heterostructures, 2019
S. Picozzi, A. Continenza, A. J. Freeman
In the pseudopotential methods, a different approach is followed [57-60] in both the semi-empirical [55,56] or first-principles (i.e., without any dependence on experimental data, but only on the atomic species involved and on fundamental constants) forms: the core electrons and the atomic nucle.us are replaced by a smooth pseudopotential, which becomes the actual potential at a certain cut-off radius away from the atomic site. Within this approximation, all the properties relative to valence electrons are determined in the same way as in all-electron methods, but the computational cost is substantially reduced, due to the smaller number of electrons involved in the calculations. However, the number of plane waves needed to reach good convergence can still be very high in the case of deep pseudo potentials or particular geometries.
First Principles Calculations in Exploring the Magnetism of Oxide-Based DMS
Published in Jiabao Yi, Sean Li, Functional Materials and Electronics, 2018
In solid substances, the motion status of valence electrons changes at extreme extend, while the electrons of inner shell change smoothly. As Figure 7.1 depicts the wave function of valence electrons Ψ(Z/r) change rather smoothly in areas above the cutoff radius rc; while Ψ(Z/r) fluctuates greatly in inner ion cores. The strong variation reflects the orthogonality with the inner core electrons wave function. The request to be orthogonal is acting as a repulsion potential, which, to some extent, cancels out the inner attraction V(Z/r). Scientists made the primary proof based on the orthogo- nalized PW function of band calculation then brought out the concept of pseudopotential. Pseudopotential is a hypothetical potential in the ion cores, which is used to replace the real one when solving the wave equation.
First-principles study of structural, elastic, electronic and optical properties of RDX under pressure
Published in Philosophical Magazine, 2020
Sheng-Hai Zhu, Han Qin, Wei Zeng, Fu-Sheng Liu, Bin Tang, Qi-Jun Liu, Ruo-Xi Li, Yun-Dan Gan
First-principles calculations were carried out with the norm-conserving pseudopotential method. Cambridge Serial Total Energy Package code (CASTEP) [20] based on DFT was employed for the calculations. Generalised gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) [21] was used to trace the exchange-correlation energy function. The C 2s22p2, N 2s22p3, O 2s22p4 and H 1s1 electrons were particularly treated as the valence shells. The plane wave cut-off energy of 830 eV was adopted. Brillouin-zone integrations were modelled by using a Monkhorst-Pack k-point mesh [22]. The convergence criterion of the change in total energy was less than 5.0 × 10−6 eV/atom. The DFT-D method was employed to solve the van der Waals interactions in molecular crystals, where the G (Grimme) [14] corrections to GGA-PBE have been applied.
Modeling study of adhesion in the TiN/Ti, TiN/ZrN, TiN/Ti/ZrN, and TiN/Zr/ZrN layered systems
Published in The Journal of Adhesion, 2020
Victor G. Zavodinsky, Yuri G. Kabaldin
In pseudopotential approach Vext is the sum of pseudopotentials of all atoms contained in the system. Pseudopotentials approach is characterized by taking into account only valence electrons; the core electrons influence give their contribution into a so-called pseudopotential acting on valence electrons. In this work pseudopotentials were created using the FHI98pp package [56] and were tested by finding of equilibrium parameters of crystal lattices a and bulk elastic modules B. Namely, we calculated the total energies of TiN an ZrN at various volumes of the lattices cells and used these results to find the equilibrium states according the Murnagham state equation [57]
A perspective on using experiment and theory to identify design principles in dye-sensitized solar cells
Published in Science and Technology of Advanced Materials, 2018
Peter J. Holliman, Christopher Kershaw, Arthur Connell, Eurig W. Jones, Robert Hobbs, Rosie Anthony, Leo Furnell, James McGettrick, Dawn Geatches, Sebastian Metz
Modelling organic dye molecules in the gas-phase or adsorbed to a surface is the most straightforward aspect of modelling DSC devices, and is commonly done using DFT [47]. Potential issues can arise where the molecules contain heavy elements, in which case the pseudopotential might not exist. However, this can be addressed by, for example, generating them on-the-fly. Furthermore, for heavy elements spin orbit coupling needs to be included [47]. Modelling isolated dye molecules or dye-plus-anchor groups in the gas-phase enables calculation of their HOMO and LUMO levels [48], which can be combined with Langmuir adsorption isotherms to postulate the orientation of the dyes on the TiO2 surface [49].