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 [2020/08/21 10:15] (current) – external edit 127.0.0.1 | ||
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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 '' | ||
+ | |||
+ | ===== Chasing charge localization in liquid water ===== | ||
+ | |||
+ | The combination of truncated exchange and ADMM results in the most effective way to run AIMD with hybrid functionals. In some systems the difference between GGA DFT and hybrids is very large. One such systems is liquid water after ionization (i.e. charge +1), where only with hybrids the expected species (OH radicals) are formed. See [[doi> | ||
+ | |||
+ | ==== 5th task : ionized water ==== | ||
+ | |||
+ | < | ||
+ | |||
+ | adapt the admm input for water to reflect the ionized state: | ||
+ | < | ||
+ | ! Charge and multiplicity | ||
+ | LSD | ||
+ | CHARGE 1 | ||
+ | MULTIPLICITY 2 | ||
+ | </ | ||
+ | because the system is electronically very difficult initially, we'll reduce the convergence threshold '' | ||
+ | |||
+ | Note that the '' | ||
+ | |||
+ | Run single point energy calculations varying the fraction of exchange from 0.25 to 0.50, does the mulliken spin population reproduce Fig. 2 in [[doi> | ||
+ | |||
+ | For the fraction 0.5, run AIMD for about 50-100fs (if time permits), what happens with the water molecule on which the spin was localized ? Do you results agree with [[doi> | ||
===== Required files ===== | ===== Required files ===== |
exercises/2015_pitt/hfx.1425471382.txt.gz · Last modified: 2020/08/21 10:15 (external edit)