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62.4.2 Density threshold method

The density threshold truncation method is an alternative to the atom-based truncation method described in section 62.4.1. Its primary advantage is that it requires just one parameter to be adjusted for all types of molecular system and functions that are important in the long range are automatically kept. At its low truncation limit it produces the full basis embedding answer or at high truncation its limit is a result constructed from just the functions on the active embedding region. Application of this method involves slightly different input options:

When using this method, the following should be taken into consideration:
(1) The accuracy of this truncation method is sensitive to the size of the basis set. For this reason, it is recommended to use at least a triple-zeta basis set.
(2) It is recommended to use Knizia's IBO localization method, which reduces the orbital tails.
(3) For accurate HF-in-HF and DFT-in-DFT results, it is recommended to use a value for DENKEEP of less than 0.0001. This is especially important when embedding across covalent bonds.
(4) The geometry must be in Cartesian coordinates.

All publications resulting from the use of this method must acknowledge the following:

S. J. Bennie, M. Stella, T. F. Miller III and F. R. Manby, J. Chem. Phys., 143, 024105 (2015).



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