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Where innovation starts
ReaxFF parameterizationusing Metropolis MonteCarlo algorithm
Eldhose Iype ([email protected])
S.V.NedeaEnergy Technology Group
December 2, 2014
2/5
/department of mechanical engineering
Parameterization of Reax force field
◮ Quantum Chemical (DFT) data is used to parameterize the forcefield
◮ A training data set is prepared which contains the followinginformations
• Atomic charges (Mulliken)• Equilibrium bond lengths• Equilibrium bond angles• Torsion angles• Energies of the DFT optimized geometries• Heat of formation
◮ Error in the force field is then calculated
Err(p1, p2, · · · pn) =
n∑
i=1
[
xi ,QM − xi ,ReaxFF
σi
]2
2/5
/department of mechanical engineering
Parameterization of Reax force field
◮ Quantum Chemical (DFT) data is used to parameterize the forcefield
◮ A training data set is prepared which contains the followinginformations
• Atomic charges (Mulliken)• Equilibrium bond lengths• Equilibrium bond angles• Torsion angles• Energies of the DFT optimized geometries• Heat of formation
◮ Error in the force field is then calculated
Err(p1, p2, · · · pn) =
n∑
i=1
[
xi ,QM − xi ,ReaxFF
σi
]2
2/5
/department of mechanical engineering
Parameterization of Reax force field
◮ Quantum Chemical (DFT) data is used to parameterize the forcefield
◮ A training data set is prepared which contains the followinginformations
• Atomic charges (Mulliken)• Equilibrium bond lengths• Equilibrium bond angles• Torsion angles• Energies of the DFT optimized geometries• Heat of formation
◮ Error in the force field is then calculated
Err(p1, p2, · · · pn) =
n∑
i=1
[
xi ,QM − xi ,ReaxFF
σi
]2
3/5
/department of mechanical engineering
Metropolis Monte Carlo (MMC) method
◮ Calculate the error of the starting force field, Errold
◮ Make a new proposition (move) for the parameters
◮ Calculate the error of the new force field, Errnew
◮ Calculate the difference in the Error, i.e.
∆Err = Errnew − Errold
◮ Accept the move with a probability given by,
P = min [1, exp (−β∆Err)] ,where, β =1
kBT
◮ Repeat the algorithm
4/5
/department of mechanical engineering
Error vs β for a Simulated Annealing run
0
1e+06
2e+06
3e+06
4e+06
5e+06
6e+06
7e+06
1e-05 0.0001 0.001
Err
or
β
Error vs β =1/(KBT)
5/5
/department of mechanical engineering
Overview
◮ How to set-up input files (geo,trainset.in)?
◮ Optimizing water force field, MMC at low temperature
◮ Simulated annealing
5/5
/department of mechanical engineering
Overview
◮ How to set-up input files (geo,trainset.in)?
◮ Optimizing water force field, MMC at low temperature
◮ Simulated annealing
5/5
/department of mechanical engineering
Overview
◮ How to set-up input files (geo,trainset.in)?
◮ Optimizing water force field, MMC at low temperature
◮ Simulated annealing