This document provides an introduction to CASTEP software and Materials Studio. It describes CASTEP as a quantum mechanics program for modeling solid-state materials and their properties. Materials Studio is a modeling environment that includes CASTEP and allows constructing and simulating molecules, crystals, polymers and other materials using various modeling methods like quantum, atomistic, and statistical approaches. It discusses different modeling tasks in CASTEP like energy calculations, geometry optimization, and properties calculations. It also summarizes some of the other modules in Materials Studio like absorption locator, amorphous cell builder, blends module, and sorption module.
3. “ Starting in the name of Allah, the
most Merciful, the most beneficial ”
4. Introduction
• CASTEP is a state-of-the-art quantum mechanics-based program designed specifically for solid-state
materials science.
• Materials Studio is a modeling and simulation environment designed to allow to predict and
understand the relationships of a material’s atomic and molecular structure with its properties and
behavior. With it one can construct, manipulate and view models of molecules, crystalline
materials, surfaces, polymers, and mesoscale structures. Materials Studio includes quantum,
atomistic (or “classical”), mesoscale, and statistical methods that enable one to evaluate materials
at various particle sizes and time scales. It also includes tools for evaluating crystal structure and
crystal growth.
6. What is Material Studio ?
• Materials Studio is software for simulating and modeling
materials. It is developed and distributed by BIOVIA (formerly
accelyrs), a firm specializing in research software for
computational chemistry, bioinformatics, cheminformatics,
molecular dynamic simulation and quantam mechanics.
• This software is used in advanced research of various materials,
such as polymers, carbon monotubes, catalysts, metals, ceramics
by universities, research centers and high tec companies. It is a
client server model software.
9. Tasks in CASTEP
The CASTEP module allows you to perform first-principles quantum mechanical calculations in order to explore
the properties of crystals and surfaces in the solid state. CASTEP can currently perform several different tasks:
• Single-point energy calculation
• Geometry optimization
• Molecular dynamics
• Elastic constants calculations
• Transition state search
• Transition state confirmation
• Properties
Each of these calculations can be set up so that it generates specified chemical and physical properties.
An additional task, known as a properties calculation, allows you to restart a completed job to compute
additional properties that were not calculated as part of the original run.
10. CASTEP Properties
The CASTEP Properties task allows you to compute electronic, structural, and vibrational properties after the
completion of a single-point energy, geometry optimization, or dynamics run on a 3D periodic system.
The properties that can be generated by CASTEP are:
• Band Structure: Electronic eigenvalues along high symmetry directions in the Brillouin zone are calculated
non-self-consistently for both valence and conduction bands, using electronic charge densities and
potentials generated during the simulation.
• Core level spectroscopy: Electronic energies on the Monkhorst-Pack mesh of k-points and the matrix
elements for electronic interband transitions are calculated, either with or without core holes.
• Density of states: Electronic eigenvalues on a fine Monkhorst-Pack grid are calculated non-selfconsistently
for both valence and conduction bands, using electronic charge densities and potentials generated during
the simulation.
• Electron density difference: The electron density difference with respect to either a linear combination
of the atomic densities or a linear combination of the densities of sets of atoms contained in the structure
is calculated.
• Electron localization function: A simple measure of electron localization in atomic and molecular
systems.
• Electronic excitations (TD-DFT): Electronic excitations for molecules in a box calculated using the time-
dependent density functional theory (TD-DFT).
11. Cont
• NMR: Chemical shielding tensors and electric field gradients are calculated.
• Optical properties: Matrix elements for electronic interband transitions are calculated. The CASTEP
Analysis dialog can be used to generate grid and chart documents containing measurable optical
properties.
• Orbitals: Information about electronic wavefunctions is provided. This allows you to visualize 3D
distribution of various electronic states (orbitals). This information is required also for visualization of STM
profiles.
• Phonons: For phonon dispersion runs, phonon frequencies and eigenvectors along high symmetry
directions in the Brillouin zone are calculated. In the case of phonon density of states calculations, phonon
frequencies and eigenvectors are computed on a Monkhorst-Pack grid. This information is required during
analysis to display total and projected (partial) phonon densities of states. It is alsoused to calculate
thermodynamic properties including atomic displacement parameters, which allow.
• Polarizability, IR and Raman spectra: The optical (ω = ∞) and dc (ω = 0) dielectric permittivity or the
optical (ω = ∞) and static (ω = 0) molecular polarizability, along with infrared or Raman intensities
(response to an electric field in the infrared range) are calculated. Permittivity is relevant for solid
materials, while polarizability and infrared intensities are relevant to molecules prepared using
thesupercell approach.
12. Cont
• Population analysis: Mulliken analysis and Hirshfeld charge analysis is performed. Mulliken bond
populations and angular momentum-resolved atomic charges (as well as magnetic moments for
spinpolarized calculations) are calculated. Optionally, the weights required for partial density of
states (PDOS) calculations are generated. Hirshfeld atomic charges are produced.
• Stress: The stress tensor is calculated and written to a seedname.castep file. This information is
useful if, for example, you perform a geometry optimization run in which cell parameters are fixed
and you want to check how far the lattice is from equilibrium. For instance, a supercell study of a
point defect should be carried out with the fixed cell that corresponds to the theoretical ground
state of the given system. The value of the stress after geometry optimization gives an indication of
the magnitude of the elastic effects associated with the supercell approximation.
20. Why Modeling
• Structures, processes and properties are numerically simulated
fully or in part on fundamental laws of physics.
• Besides modeling stable molecules some method may be used to
model also short lived species(unstable intermediates and
transition states)
• Important in supporting or replacing experimental studies
28. Other Crystallographic Tools
Morphology: prediction of the morphology of the crystal starting from atomic structure of crystal
(crystal structure, surface stability, aids the development of tailor made additives)
Polymorph Predictor: prediction of potential polymers directly from the molecular structure.
29. Other Modules in Material Studio
• Absorption locator
• Amorphous cell
• Blends
• Conformers
• Scripting
• Sorption
36. CASTEP Modeling Disorders
Many crystal structures possess static positional disorder. Materials Studio allows you to model
disorder by defining mixture atoms.
Mixture atoms
Atomic sites in a disordered crystal can be described in terms of a hybrid atom, which consists of two
or more element types. The relative concentrations can be set for any number of atoms, where the
total concentration must be 100%. The mixture atoms description is the most often used
representation of solid solutions, metallic alloys, disordered minerals, and so on.
37. Technical limitations
Current implementation of the molecular dynamics (MD) algorithms in CASTEP is not yet compatible
with the virtual crystal approximation (VCA) formalism, which is used to model disorder in solids. None
of the MD schemes (NVE, NPT, and so on) work for disordered crystals in the current version.
The following properties are unavailable for disordered systems:
• Population analysis
• Vibrational properties (phonon dispersion, phonon density of states)
• Optical properties
In addition, geometry optimization based on damped MD is not available (since MD itself is not
allowed).
Atom occupancy cannot be used with the current CASTEP implementation of the virtual crystal
approximation (VCA). Partial atom occupancy can be considered as a special case of a mixture atom,
where one part of the mixture is an atom of "nothing". This case is not supported for a number of
technical and fundamental reasons.
38. Cont
The limitations listed above fall into three categories:
• Properties that are ill-defined or do not make sense at all for mixture atoms (population analysis,
vibrational properties).
• Features where the calculations might be possible, but which require more theoretical work
(optics, partial atomic occupancies).
• Features that are blocked for purely technical reasons (molecular dynamics).
These limitations are imposed by the user interface; if you attempt a run using a combination of
settings which is not allowed, a message box explaining why the run cannot be carried out will be
displayed when you select Run or Save Files.
