exercises:2015_pitt:hfx
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exercises:2015_pitt:hfx [2015/03/04 12:16] – [Truncated Coulomb operator] vondele | exercises:2015_pitt:hfx [2015/03/05 09:02] – [4rd task : introduce ADMM] vondele | ||
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* How to detect instabilities due to too aggressive screening. | * How to detect instabilities due to too aggressive screening. | ||
- | Question: What is the HOMO-LUMO gap for this configuration ? How does this compare to the GGA result ? | + | Question: What is the HOMO-LUMO gap for this configuration ? How does this compare to the GGA result |
===== Truncated Coulomb operator with long range correction ===== | ===== Truncated Coulomb operator with long range correction ===== | ||
+ | Like in the HSE functional, the difference between the operator used for exchange and 1/r, can be accounted for by a special GGA exchange functional. Also for the truncated coulomb operator this is possible, and allows for xc functionals that embed very short range exchange operators only. This can be used to speedup the calculation, | ||
+ | |||
+ | ==== 3rd task ==== | ||
+ | |||
+ | Add to the & | ||
+ | |||
+ | < | ||
+ | & | ||
+ | | ||
+ | | ||
+ | & | ||
+ | </ | ||
+ | |||
+ | and employ the same '' | ||
+ | |||
+ | Rerun the single point energy calculation and note the band gap. | ||
+ | * Is such a short range sufficient to have a sizable effect on the band gap ? | ||
+ | * is '' | ||
===== Auxiliary Density Matrix Methods (ADMM) ===== | ===== Auxiliary Density Matrix Methods (ADMM) ===== | ||
+ | |||
+ | ADMM is an approach to mitigate the cost of HFX for large basis sets. In particular, if MOLOPT basis sets are used, standard HFX becomes too expensive (CP2K can not deal efficiently with highly contracted AOs). In ADMM, an '' | ||
+ | |||
+ | ==== 4rd task : introduce ADMM ==== | ||
+ | |||
+ | Make the following changes: | ||
+ | * insert and additional line '' | ||
+ | * insert for each ''& | ||
+ | * insert a secion ''& | ||
+ | |||
+ | < | ||
+ | ! use ADMM | ||
+ | & | ||
+ | ! recommended, | ||
+ | ! each kind will need an AUX_FIT_BASIS_SET. | ||
+ | METHOD BASIS_PROJECTION | ||
+ | ! recommended, | ||
+ | ! can be expensive for large systems | ||
+ | ADMM_PURIFICATION_METHOD MO_DIAG | ||
+ | &END | ||
+ | </ | ||
+ | |||
+ | < | ||
+ | |||
+ | < | ||
+ | |||
+ | Run the input, what's the '' | ||
+ | |||
===== Required files ===== | ===== Required files ===== |
exercises/2015_pitt/hfx.txt · Last modified: 2020/08/21 10:15 by 127.0.0.1