Setup tab

The Setup tab allows you to choose the type and quality of calculation that CASTEP performs, and other basic input options such as exchange-correlation functional, spin polarization, and total charge.

Task: Select the type of calculation for CASTEP to perform. Available options are:

Energy - performs a single-point energy calculation.
Geometry Optimization - searches for a minimum energy structure.
Dynamics - performs a molecular dynamics calculation.
Elastic Constants - performs an elastic constants calculation.
TS Search - performs a transition state search.
TS Confirmation - produces a refined reaction path based on a TS search.
Properties - calculates properties based on the results obtained from one of the other tasks.

More...: Provides access to further options for the selected task: opening the CASTEP Geometry Optimization, CASTEP Dynamics, CASTEP Elastic Constants, CASTEP Transition State Search , or CASTEP TS Confirmation dialogs.

Quality: Select the overall quality of a single-point energy, geometry optimization, or dynamics calculation. This quality affects the basis set, k-point, and SCF convergence criteria, along with the convergence criteria for the Geometry Optimization, Elastic Constants, and TS Search tasks. Available options are:

Express
Coarse
Medium
Fine
Ultra-fine

Use the Coarse quality setting for a quick assessment of the calculation. Use the Express quality to achieve a good compromise between speed and accuracy that is appropriate for most calculations. Use Fine and Ultra-fine quality settings for calculations that require very high accuracy, at the expense of longer calculation times. Carry out convergence testing for highly sensitive calculations by increasing the quality setting and possibly by increasing the accuracy of the basis set and the k-point sampling.

The Quality setting affects all relevant task parameters that control the precision of the simulation. If any parameter has a value different from that specified by the overall quality level, the Quality displays as Customized.

Functional: Select the type of DFT exchange-correlation potential to use in the calculation. Choose the class of functional from the first list, then select the specific functional from the second list.

LDA: local functional
- CA-PZ: Ceperley and Alder, 1980; data as parameterized by Perdew and Zunger, 1981
GGA: gradient-corrected functionals
- PBE: Perdew et al., 1996
- RPBE: Hammer et al., 1999
- PW91: Perdew et al., 1992
- WC: Wu and Cohen, 2006
- PBESOL: Perdew et al., 2008
- BLYP: exchange from Becke, 1988; correlation from Lee, Yang, Parr, 1988
m-GGA: meta-GGA functional
- RSCAN: Bartók and Yates, 2019; regularized version of the SCAN functional by Sun et al., 2016
Nonlocal: Nonlocal functionals
- HF
- HF-LDA
- sX
- sX-LDA
Hybrid: Hybrid functionals
- PBE0
- B3LYP
- HSE03
- HSE06

The m-GGA functional is not compatible with spin-orbit coupling, J-coupling, linear-response phonons, or polarizability calculations. You cannot use this formalism with mixture atoms. You can only use on-the-fly generated pseudopotentials with m-GGA.
You can only use Nonlocal and Hybrid functionals for insulators using All Bands/EDFT Electronic minimizer tasks. They are not compatible with NMR, phonon, or polarizability calculations. You cannot use these formalisms with mixture atoms. You can only use norm-conserving potentials with Nonlocal and Hybrid.
There is an important difference between standard DFT calculations with local exchange-correlation potentials and the nonlocal exchange case. The potential used in the latter scenario depends on the wavefunctions at SCF k-points, while in the former case, the potential depends only on electron density. This difference can make calculations a lot more expensive in terms of memory usage and CPU time, so it is advisable to limit the number of SCF k-points that you use in such situations. This is particularly relevant for small unit cells, where the default settings may generate a very large k-point set.

Use method for DFT-D correction: When selected, dispersion corrections use the chosen method. Available options are:

TS for GGA PBE, PBESOL, RPBE, BLYP, PW91; also for PBE0 and B3LYP
Grimme for GGA PBE, GGA BLYP, and B3LYP
OBS for GGA PW91 and LDA
MBD* for GGA PBE; also for HSE03, HSE06, and PBE0

The option selected automatically updates the Use custom DFT-D parameters option on the DFT-D tab of the CASTEP Electronic Options dialog.

Spin polarization: Select how to treat spin density. Available options are:

Non-polarized also known as 'spin-restricted' calculation, uses the same orbitals for alpha and beta spins.
Collinear also known as 'spin-unrestricted' calculation, separate calculation for majority and minority spin projections.
Non-collinear the calculation allows spin density to vary the quantization axis in each point of space.

Use formal spin as initial: When selected, indicates that calculation takes the initial value for the number of unpaired electrons from the formal spin specified for each atom. The calculation optimizes this starting value. If you do not select this option, you can specify the initial value for the number of unpaired electrons. Default = checked.

This option is enabled only if the Spin polarization is Non-collinear or Collinear.

CASTEP only uses atom-resolved initial spin if the Electronic minimizer is Density mixing on the SCF tab of the CASTEP Electronic Options dialog or if you select DFT+U.

Use DFT+U: When checked, CASTEP uses DFT+U (also known as the LDA+U formalism). You can specify the actual values of U on the Hubbard U tab of the Electronic Configuration dialog.

The DFT+U formalism is not compatible with NMR or polarizability calculations. You cannot use this formalism with mixture atoms or real-space pseudopotentials.

Include spin-orbit coupling: When select, adds spin-orbit coupling to the Hamiltonian.

Note: This option is only enabled if the Spin polarization is Non-polarized or Non-collinear. The formalism is implemented for norm-conserving pseudopotentials, either on-the-fly generated or tabulated, with no LDA+U corrections. In addition, it is not compatible with calculations of:

NMR
Dipole corrections
Electron localization function
Linear response, including polarizability calculation
Electronic excitations
Partial density of states
Hirshfeld population analysis

Visualization of the electrostatic potential is also not yet implemented.

Metal: When selected, this indicates that the system is metallic so that empty bands can be created and edited. When this is not selected, the Fix occupancy checkbox on the SCF tab of the CASTEP Electronic Options dialog is checked. When this is not selected, the k-point separations used by default are coarser. Default = checked.

In some calculations, it is not sufficient to use fixed orbital occupancies if DFT results indicate that the system under investigation has a band gap. This applies to calculations that use the linear response formalism for vibrational properties and to calculations of electric field responses (polarizability and IR and Raman spectra). Attempting to study a metallic systems using fixed orbital occupancies results in poor convergence and usually in unphysical results for IR and Raman intensities and for polarizability. If this is the case, verify whether your system is metallic by running either density of states or band structure calculations.

Charge: Specify the total charge on the unit cell.

Access methods

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Setup tab

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