Example: Cu_slab: 2-dim. Finite temperature and orbital plot¶
A two-dimensional infinite (periodic boundary conditions) slab calculation is performed for Cu. The dimensionality is simply defined by the number of records in the Lattice data block. In a 2-dimensional calculation the lattice vectors are put in the xy-plane.
Slab calculations for metals frequently suffer from SCF convergence problems, as a result of the open valence band(s). To help the program converge it is often useful or even necessary to use some special features, such as the ElectronicTemperature key. This particular key requires a numerical value (0.025 in the example) and implies that a finite-temperature electronic distribution is used, rather than a sharp cut-off at the Fermi level. The numerical value is the applied energy width, in Hartree units.
The so-modified electronic distribution also affects the energy. The ‘true’ zero-T energy is computed, approximately, by an interpolation formula. The interpolation is not very accurate and one should try to use as small as possible values for the ElectronicTemperature key so as to avoid increasing uncertainty in the results. The program prints, in the energy section of the output file, the finite-T correction term that has been applied through the interpolation formula. This gives at least an indication of any remaining uncorrected deviation of the outcome from a true zero-T calculation.
In the second run the RUNKF file of the first run is used to do an orbital plot restart. Normally you would rename the resulting TAPE41 to ‘myslab.t41’ and watch the orbitals with ADFview.
# ----------------------------- first run -------------------------- $ADFBIN/band << eor Title Cu slab Comment Technical Quadratic K space integration Good real space integration accuracy Features Lattice : 2D Unit cell : 1 atom, 1x1 Basis : NO+STO w/ core Options : ElectronicTemperature (temperature effect) End Kspace 5 Accuracy 4 Convergence ElectronicTemperature 0.025 End Lattice 4.822 0.0 0.0 4.822 End Atoms Cu 0.0 0.0 0.0 End BasisDefaults BasisType DZ End EndInput eor mv RUNKF CuSlab.runkf rm Points # ----------------------------- orbital plot -------------------------- export NSCM=1 $ADFBIN/band -n 1 << eor Title Cu slab orbital plot Comment Technical Quadratic K space integration Good real space integration accuracy Features Lattice : 2D Unit cell : 1 atom, 1x1 Basis : NO+STO w/ core Options : ElectronicTemperature (temperature effect) End Kspace 5 Accuracy 4 Restart File CuSlab.runkf OrbitalPlot End Grid Type Coarse End OrbitalPlot 1 Band 2 4 ! k-point 1, bands 2 to 4 3 -0.1 0.1 ! k-point 3 orbitals within 0.1 Hartree from Fermi Level End Convergence ElectronicTemperature 0.025 End Lattice 4.822 0.000 0.000 4.822 End Atoms Cu 0.0 0.0 0.0 End BasisDefaults BasisType DZ End EndInput eor echo "Begin TOC of tape41" $ADFBIN/dmpkf -n 1 TAPE41 --toc echo "End TOC of tape41"