exercises:common:sgcp
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exercises:common:sgcp [2025/06/19 02:28] – jglan | exercises:common:sgcp [2025/06/19 02:54] (current) – [2. Comparison with CPMD and BOMD] jglan | ||
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[[ https:// | [[ https:// | ||
- | ===Introduction=== | + | ====1. Introduction==== |
Second Generation CPMD (2ndG CPMD) is a molecular dynamics method that combines the efficiency of Car-Parrinello MD (CPMD) with the accuracy of Born-Oppenheimer MD (BOMD). It avoids fully self-consistent field (SCF) optimizations at each time step while enabling larger integration steps and maintaining accuracy close to BOMD. | Second Generation CPMD (2ndG CPMD) is a molecular dynamics method that combines the efficiency of Car-Parrinello MD (CPMD) with the accuracy of Born-Oppenheimer MD (BOMD). It avoids fully self-consistent field (SCF) optimizations at each time step while enabling larger integration steps and maintaining accuracy close to BOMD. | ||
- | | Feature | + | |
- | |----------------------------------|---------------|--------------|--------------------------| | + | **Goal:** Retain the efficiency of CPMD while achieving BOMD-level accuracy. |
- | | SCF at each step | + | |
+ | - **Efficiency**: | ||
+ | |||
+ | - **Accuracy**: | ||
+ | |||
+ | - **Stability**: | ||
+ | |||
+ | - **Error Control**: | ||
+ | |||
+ | ====2. Comparison with CPMD and BOMD==== | ||
+ | |||
+ | | Feature | ||
+ | | SCF at each step | No | Yes | | ||
| Time step | Small (~0.1 fs) | Large (~1 fs) | Large (~1–2 fs) | | | Time step | Small (~0.1 fs) | Large (~1 fs) | Large (~1–2 fs) | | ||
| Conserved quantity preservation | | Conserved quantity preservation | ||
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| Works for small-gap systems | | Works for small-gap systems | ||
+ | ====3. ASPC Method==== | ||
+ | ASPC Method: Always Stable Predictor Corrector | ||
+ | |||
+ | ASPC is a **Gear-type integrator** for electronic wavefunctions: | ||
+ | |||
+ | Predictor: | ||
+ | |||
+ | \[ | ||
+ | C_p(t_n) = \sum_{m=1}^{K} (-1)^{m+1} \cdot m \cdot B_m \cdot P_S(t_{n-m}) | ||
+ | \] | ||
+ | |||
+ | where: | ||
+ | - Bm: Kolafa predictor coefficients | ||
+ | - PS: projection onto the overlap matrix S | ||
+ | |||
+ | Corrector: | ||
+ | |||
+ | \[ | ||
+ | C(t_n) = \omega \cdot \min[C_p(t_n)] + (1 - \omega) \cdot C_p(t_n), \quad \omega = \frac{K}{2K - 1} | ||
+ | \] | ||
+ | |||
+ | Langevin Dynamics & Dissipation Compensation | ||
+ | |||
+ | Because ASPC introduces small dissipation, | ||
+ | |||
+ | \[ | ||
+ | M_I \ddot{R}_I = F_\text{BO} - (\gamma_D + \gamma_L)\dot{R}_I + \Xi_I | ||
+ | \] | ||
+ | |||
+ | - γD: implicit friction from ASPC | ||
+ | - γL: Langevin thermostat | ||
+ | - ΞI: Langevin random noise | ||
+ | |||
+ | |||
+ | |||
+ | ====4. How to Set Up in CP2K==== | ||
+ | |||
+ | |||
+ | | Parameter | ||
+ | | EXTRAPOLATION_ORDER | ||
+ | | MAX_SCF_HIST | ||
+ | | STEPSIZE | ||
+ | | PRECONDITIONER | ||
+ | | NOISY_GAMMA (γ_D) | ||
+ | | GAMMA (γ_L) | ||
+ | |||
+ | 1. ASPC Extrapolation | ||
+ | |||
+ | & | ||
+ | &DFT | ||
+ | & | ||
+ | EXTRAPOLATION ASPC | ||
+ | EXTRAPOLATION_ORDER 0 # Higher gives better corrector | ||
+ | & | ||
+ | & | ||
+ | MAX_SCF_HIST 2 | ||
+ | & | ||
+ | &END DFT | ||
+ | &END FORCE_EVAL | ||
+ | |||
+ | 2. Langevin Thermostat | ||
+ | |||
+ | &MOTION | ||
+ | &MD | ||
+ | ENSEMBLE LANGEVIN | ||
+ | & | ||
+ | GAMMA 0.005 ! γ_L | ||
+ | NOISY_GAMMA 4.0E-4 | ||
+ | &END LANGEVIN | ||
+ | &END MD | ||
+ | &END MOTION | ||
+ | |||
+ | 3. Atom-Specific γ_D (Optional) | ||
+ | |||
+ | & | ||
+ | DO_LANGEVIN_DEFAULT TRUE | ||
+ | & | ||
+ | TEMPERATURE 500 | ||
+ | NOISY_GAMMA_REGION 4.E-4 | ||
+ | LIST 577..745 | ||
+ | &END DEFINE_REGION | ||
+ | &END THERMAL_REGION | ||
exercises/common/sgcp.1750300081.txt.gz · Last modified: by jglan