howto:kg
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- | ====== How to run simulations with Kim-Gordon method ====== | + | This page has been moved to: https://manual.cp2k.org/trunk/methods/embedding/kim-gordon.html |
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- | ===== Introduction ===== | + | |
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- | This method is based on density embedding. Let's introduce first the subtraction scheme definition of the density embedding method: | + | |
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- | Etot=EHK[ρtot]−∑AEHK[ρA]+∑AEKS[ρA]. | + | |
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- | The total electronic density ρtot=∑AρA is the sum over all the subsystems A of the subsystem densities ρA. The energy functionals EHK and EKS are the Hohenberg–Kohn and the Kohn–Sham functionals, | + | |
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- | EHK[ρ]=THK[ρ]+EHKext[ρ]+12∫∫ρ(r)ρ(r′)r−r′drdr′+EXC[ρ].\\ | + | |
- | EKS[P]=TS[P]+Eext[P]+12∫∫ρ(r)ρ(r′)r−r′drdr′+EXC[ρ]. | + | |
- | + | ||
- | where P is the reduced one-particle density matrix of the system. First of all, it's important | + | |
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- | EHKext[ρtot]=∑AEHKext[ρA]. | + | |
- | + | ||
- | Now, calling the classical Coulomb term Ehxc[ρ] and defining the non-additive kinetic energy as Tnadd[ρ,ρA]=THK[ρ]−∑ATHK[ρA], | + | |
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- | Etot[PA]=∑A(TS[PA]+Eext[PA])+Ehxc[ρ]+Tnadd[PA]. | + | |
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- | To avoid the integration of the kinetic energy functional for each subsystem, an atomic potential approximation can be applied. For a local potential: | + | |
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- | Tnadd=TS[ρ]−∑ATS[ρA]=\\ | + | |
- | ∫ρμ[ρ]dr−∑a∫ρAμ[ρA]dr=\\ | + | |
- | ∑a∫ρA(μ[ρ]−μ[ρA])dr | + | |
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- | Making a linearization approximation for the functional μ[ρ] | + | |
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- | μ[ρ]−μ[ρA]∼∑B≠A∂μ[ρA]∂ρρB=μ′[ρA]\\ | + | |
- | Tnadd=∑ATS∑B≠A∫μ′[ρA]ρAρBdr | + | |
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- | A further approximation of the derivative functional in atomic contributions is: | + | |
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- | μ′[ρA]ρA=VK[ρA]∼∑a∈AVKa(Ra) | + | |
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- | The realization that a typical kinetic energy functional is proportional to $\rho^{5/3}$ leads to a model for the final atomic local potential of the form: | + | |
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- | $\displaystyle V_{a}^{K}(R_{a}) = N_{a}\rho_{a}^{2/3}$ | + | |
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- | where ρa is a model atomic density. Such local potential can help to speed up the underlying embedding calculation. | + | |
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- | ===== CP2K tutorial ===== | + | |
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- | The division of the total system into subsystems is a critical point, in order to do that properly it is important to specify which is the ' | + | |
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- | < | + | |
- | & | + | |
- | &CELL | + | |
- | ABC 9.8528 9.8528 9.8528 | + | |
- | &END CELL | + | |
- | & | + | |
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- | ... | + | |
- | &END COORD | + | |
- | & | + | |
- | CONN_FILE_FORMAT USER | + | |
- | &END | + | |
- | </code> | + | |
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- | This strategy is based on the fourth column in the COORD section. At this point the code is able to find the best combination of ' | + | |
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- | < | + | |
- | & | + | |
- | MAX_SCF | + | |
- | EPS_FILTER | + | |
- | EPS_SCF | + | |
- | MU | + | |
- | PURIFICATION_METHOD TRS4 | + | |
- | &END | + | |
- | </code> | + | |
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- | This speeds up the calculation, | + | |
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- | < | + | |
- | &QS | + | |
- | LS_SCF | + | |
- | KG_METHOD | + | |
- | ... | + | |
- | &END QS | + | |
- | </note> | + | |
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- | Once all these passages are done, one has to choose the TNADD_METHOD. For the first type of calculation, | + | |
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- | < | + | |
- | &XC | + | |
- | & | + | |
- | & | + | |
- | FUNCTIONAL T92 # | + | |
- | &END | + | |
- | &END | + | |
- | &END | + | |
- | </code> | + | |
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- | And in the same section others corrections can be added (example: VDW_POTENTIAL).\\ | + | |
- | For the second type of calculation the keyword to select is ATOMIC. This method implies a supplemental atomic potential (create a file which contains all the required potentials). These templates of potentials can be found inside the tests > QS > regtest-kg folder of the CP2K and they can be generated directly from the code (look at tests > ATOM > regtest-pseudo > O_KG.inp). It's important to point out that this method is still in the experimental stage and further investigations are needed. | + | |
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- | < | + | |
- | </ | + |
howto/kg.1544188651.txt.gz · Last modified: 2020/08/21 10:15 (external edit)