Motivation Force Field Tuning [MMIM][Cl] Conclusion Modeling Room Temperature Ionic Liquids by Classical Molecular Dynamics Simulations Florian Dommert ICP - Institute for Computational Physics University Stuttgart NSASM 2010 F. Dommert Classical MD Simulations of Ionic Liquids
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Motivation Force Field Tuning [MMIM][Cl] Conclusion
Modeling Room Temperature Ionic Liquidsby Classical Molecular Dynamics Simulations
Florian Dommert
ICP - Institute for Computational PhysicsUniversity Stuttgart
NSASM 2010
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Outline
1 Motivation
2 Force Field Tuning
3 Dimethylimidazolium chloride [MMIM][Cl]
4 Conclusion
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Outline
1 Motivation
2 Force Field Tuning
3 Dimethylimidazolium chloride [MMIM][Cl]
4 Conclusion
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Room Temperature Ionic Liquids
Class of salts that are liquid at room temperature
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Nonbonded Interactions
The Blöchl method [JCP 103, 7422 (1995)]Idea: Multipole expansion of the charge density
QL =
∫V
rLYL(r)nV (r) dV
Model charge density nV (r) composed of Gaussians gi :
nV (r) =∑
i
qigi(r), with gi(r) =1(√πrc,i
)3 exp
(−(
r − Ri
rc,i
)2)
Method of Lagrangian multipliers to obtain nV (r) in rec. spacewith w = 4π(G2 −G2
c)/(GcG)2, for |G| < Gc , and 0 elsewhere:
F (qi , λ) =V2
∑G 6=0
w(G)
∣∣∣∣∣n(G)−∑
i
qigi(G)
∣∣∣∣∣2
− λ
[n(0)V −
∑i
qigi(0)V
]
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Nonbonded Interactions
Short range interactions
most time consuming part of force fieldparametrization
dependent on charge distributiondihedral parametrization affected by short rangeinteractions“simple” technique not available
iterative methods to incorporate missing interactions
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Short range interactions
Iterative adaption of force field parameters by MD
Target properties
experimental density at different temperaturesradial distribution given by “ab–initio” MD simulations
Adaption procedure1 sampling of a small part of the parameter space2 determination of a target error function ε3 minimization of ε→ new starting point for step 1
Tuning of the force field up to a certain accuracy
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Short range interactions
Sampling of the parameter space
Simulations of varying parameters around a reference point
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Force field tuning
RDF
0.2 0.3 0.4 0.5 0.6 0.7 0.8Distance / nm
0.0
0.5
1.0
1.5
2.0
2.5
g(r)
H3 -ClCLaPBLFFC,NBTFFCPMD
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Distance / nm
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5H1 -Cl
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Force field tuning
Coordination number
0.2 0.3 0.4 0.5 0.6 0.7 0.8Distance / nm
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Coor
dina
tion
num
ber
H3 -ClCLaPBLFFC,NBTFFCPMD
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Distance / nm
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5H1 -Cl
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Force field tuning
Final force field
partial charges from Blöchlbonded interactions from CLaPadapted dihedral potentials to chargestuned short-range parameters
→ Validation of tuned parameters
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Validation
Conductivity
0 100 200 300 400 500Time / ps
0
1
2
3
4
5
6
7∆
MJ /
6 V
k B T
·10−
9 /
Sm−
1ps
σexp.=10.65 Sm−1
CLaP σ=0.48 Sm−1
BLFF σ=14.19 Sm−1
C,N σ=0.70 Sm−1
BTFF σ=8.64 Sm−1
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Outline
1 Motivation
2 Force Field Tuning
3 Dimethylimidazolium chloride [MMIM][Cl]
4 Conclusion
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Classical MD simulations allow to accessmacroscopic properties of ionic liquids
suitable force field required→ force field tuning for Blöchl charges
adaption to static properties allows description of dynamiconesinformation obtained on different scales allows to setup aforce field for ionic liquids straightforwardly
F. Dommert Classical MD Simulations of Ionic Liquids
Motivation Force Field Tuning [MMIM][Cl] Conclusion
Acknowledgment
DFG SPP 1191 for fundingHöchstleistungsrechenzentrum Stuttgart (HLRS) for thehuge amount of computer timethe members of the Multiscale project (AGs Delle Site,Berger, Holm)the GROMACS developer team for providing a fast, freeand flexible simulation tool
F. Dommert Classical MD Simulations of Ionic Liquids