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 overrides 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 you request the calculation of linear response properties, CASTEP uses a convergence threshold of 10^-8 eV atom^-1, unless the specified threshold is lower. To force CASTEP to use a less stringent threshold, manually add the ELEC_ENERGY_TOL parameter to 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 ends after the specified number of iterations, even if the SCF has not converged.

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

Electronic minimizer: Specify the electronic minimization method to use 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, use the EDFT scheme for metallic systems where converging electronic structure using the Density Mixing option proves problematic.

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

Available only when you select the Density Mixing minimization method.

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

Available 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.

Available only when you select the Density Mixing minimization method.

Fix occupancy: When selected, this fixes thee electronic occupation numbers during electronic minimization. CASTEP includes only the lowest occupied states 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 list. Available options are:

None (default)
Non self-consistent
Self-consistent

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.

It is recommended to use the All Bands/EDFT electronic minimization scheme when applying a self-consistent dipole correction to an elongated cell of a slab representing a metal surface; the Density mixing minimization scheme may fail to converge for such systems.

Use Non self-consistent for cases where it is hard to converge the SCF with Apply dipole corrections. You can only use this option for Energy calculations, it is not compatible with phonon calculations.

CASTEP applies dipole corrections only if the system is either molecule in the box or a periodic slab with the vacuum layer of at least 8 Å.

To apply dipole corrections, CASTEP converts the symmetry of the system 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

SCF tab

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