CASTEP > Dialogs in CASTEP > CASTEP Calculation dialog > Electronic tab > CASTEP Electronic Options dialog > SCF tab - CASTEP Electronic Options dialog

SCF tab

The SCF tab on the CASTEP Electronic Options dialog provides access to parameters that control the electronic minimization algorithm.

SCF tolerance: Specify the SCF convergence threshold. This will override the SCF tolerance option specified on the Electronic tab.

When calculating linear response properties (for example phonons, polarizabilities, NMR properties), it is important that the SCF convergence threshold is sufficiently strict from the computational point of view to accurately calculate these properties. When the calculation of linear response properties is requested, CASTEP will use a convergence threshold of 10-8 eV atom-1, unless the specified threshold is lower. To force CASTEP to use a less stringent threshold, the ELEC_ENERGY_TOL parameter should be manually inserted in the input parameters (.param) file for the property calculation.

Max. SCF cycles: Set the maximum number of SCF iterations allowed for an energy calculation. The energy calculation will end after the specified number of iterations, even if the SCF has not converged.

Convergence window: The convergence tolerance window for SCF. This is number of SCF iterations in a row for which convergence criteria are fulfilled. This parameter is required in order to avoid occasional oscillations.

Electronic minimizer: Specify the electronic minimization method to be used for the SCF calculation. Two options are available, Density Mixing and All Bands/EDFT.

The Density Mixing option is recommended, particularly for variable occupancy calculations. The All Bands/EDFT method is usually slower and requires more memory. However, the EDFT scheme is recommended for metallic systems where converging electronic structure using Density Mixing option proves problematic.

Charge: Specify the amplitude for charge density mixing (i.e., the amplitude of the output charge density to mix with the input charge density to obtain input for the next iteration).

This option is enabled only if the Density Mixing minimization method is selected.

Spin: Specify the amplitude for spin density mixing, i.e. the amplitude of the output spin density to mix with the input spin density to obtain input for the next iteration.

This option in enabled only for spin-polarized calculations using the Density Mixing minimization method.

More...: Provides access to the CASTEP Density Mixing Options dialog, where more detailed control over the Density Mixing electronic minimization method is available.

This option is enabled only if the Density Mixing minimization method is selected.

Fix occupancy: When checked, the electronic occupation numbers will be fixed during electronic minimization. Only the lowest, occupied states will be included in the calculation. Default = checked.

More...: Provides access to the CASTEP Occupancy Options dialog, where more detailed control over the occupancies is available.

Apply dipole corrections: Select the type of dipole corrections to apply from the dropdown list. Available options are:

Self-consistent is the most accurate option, as this affects the electrostatic potential as well as the total energy and its gradients. This is the only option that is suitable to investigate the effect of dipole corrections, for example on surface workfunctions.

Non self-consistent is recommended for cases where it is hard to converge the SCF with Apply dipole corrections set. This option can only be used for Energy calculations and is not compatible with phonon calculations.

Dipole corrections will be applied only if the system is either molecule in the box or a periodic slab with the vacuum layer of at least 8 Å.

If dipole corrections are to be applied the symmetry of the system will be converted to P1 to bring the molecule (or slab) into the center of the unit cell.

Access methods

Menu Modules | CASTEP | Calculation | Electronic | More... | SCF
Toolbar | Calculation | Electronic | More... | SCF
See Also:

Self-consistent electronic minimization
Setting electronic options
Electronic tab - CASTEP Calculation dialog
Basis tab - CASTEP Electronic Options dialog
k-points tab - CASTEP Electronic Options dialog
Potentials tab - CASTEP Electronic Options dialog
CASTEP Density Mixing Options dialog
CASTEP Occupancy Options dialog
Self-consistent electronic minimization

Accelrys Materials Studio 8.0 Help: Wednesday, December 17, 2014
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