The program CELSLC is used to calculate object transmission functions aka. phase gratings from atomic structure models. Files describing the atomic structure and other parameters are specified as arguments upon calling. The output is oganized in so-called slice files, which are input for multislice calculations with the program MSA or the Dr. Probe GUI.
CELSLC
In order to calculate the elastic forward scattering of the incident electron by the electrostatic potential of the atomic structure, the crystal potential is projected to planes from very thin volume slices in the multislice approach. The elastic scattering potentials are calculated using the parameterization of Weickenmeier and Kohl [Acta Cryst. A47 (1991) p. 590-597]. CELSLC allows you also to use alternative atomic form factors. Please contect the developer if you are interested.
Projected potentials of each structure slice are transformed to phase gratings describing the phase shift of the probing eletcron wave function caused by the screened Coulomb potentials of the atomic core charges. Thermal vibration models using the frozen-lattice approach or Debye-Waller factors are implemented.
Two different options are provided to apply absorptive potentials:
1. Absorptive potentials according to Weickenmeier and Kohl [Acta Cryst. A47 (1991) p. 590-597] describing the loss of electrons in the elastic channel. The option is available when applying Debye-Waller factors.
2. Constant user defined absorption parameter, as proposed by Hashimoto, Howie, and Whelan [Proc. R. Soc. London Ser. A, 269 (1962) p. 80-103] describing a loss of electrons relative to the scattering strength of an atom. Typical values are on the range from 0.01 to 0.20.
Example: Frozen-lattice variants of periodic SrTiO3 [001] for HAADF-STEM image simulations
50 frozen-lattice variants are calculated for each of 2 structure slices on a 480 x 480 grid for 300 keV. The input structure model consists of 3 x 3 unit cells. The output phase gratings will be stored in the files STO001-300kV_001.sli and STO001-300kV_002.sli.
celslc -cel STO_001_3x3.cel -slc STO001-300kV -nx 480 -ny 480 -nz 2 -nv 50 -fl -ht 300
Example: Periodic SrTiO3 [110] for high-resolution TEM image simulations
Phase gratings are calculated of 4 structure slices are calculated on a 108 x 80 grid for 300 keV electrons with Debye-Waller factors and absorptive form factors. The input structure model consists of 2 SrTiO3 unit cells in [110] orientation. The output phase gratings will be stored in the files STO100-300kV_001.sli, …, STO100-300kV_004.sli.
celslc -cel STO_110_2UC.cel -slc STO110-300kV -nx 108 -ny 80 -nz 4 -dwf -abs -ht 300