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Core treatment The Core treatment parameter controls how electrons in the lowest lying atomic orbitals are treated. The default setting, All Electron, treats these in the same manner as valence electrons, and is appropriate for atoms up to about atomic number 36 (Kr). With heavier elements, relativistic effects become important in the core electrons. One method of incorporating these effects is to use the All Electron Relativistic option. As the name implies, the core electrons are still included in the calculation, but scalar relativistic effects are included (Koelling and Harmon, 1977; Douglas and Kroll, 1974). This yields a more accurate calculation, but increases the computational cost. An alternative to all-electron calculations is to use DFT Semi-core Pseudopots (DSPP; Delley, 2002) or Effective Core Potentials (ECP; Dolg et al., 1987; Bergner et al., 1993). These replace the effects of core electrons with a simple potential. Because the core electrons are dropped, the calculation is less computationally expensive, but because these core potentials include some degree of relativistic effects, they can be very useful approximations for heavier elements. You cannot restrict the use of ECPs or DSPPs to specific elements. Whenever you use either option, DMol3 examines a data file that contains the potentials. If DSPP or ECP data are found for an element, then the core electrons for that element are replaced; if the data are not found for an element, then all its electrons are retained. Currently, DSPPs and ECPs are provided beginning with element number 21, Sc. For example, in a system containing H, O, Al, Cu, and Au, if you opt to use ECPs or DSPPs, only the core electrons for Cu and Au will be replaced; H, O, and Al will be treated as in the all-electron case. When it is necessary to use one of these approximations, Accelrys recommends that you use DSPPs rather than ECPs. The former have been developed specifically for DMol3 calculations, whereas the latter are Hartree-Fock potentials. To set the type of core treatment, choose All Electron, Effective Core Potential, All Electron Relativistic, or DFT Semi-core Pseudopots from the Core treatment dropdown list. Real space cutoff |
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