AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Activities in Theoretical Chemistry:Atomistic Simulations
E. Spohr
Lehrstuhl für Theoretische Chemie, Universität Duisburg-EssenUniversitätsstr. 5D-45141 Essen
[email protected]://www.uni-due.de/chemie/ak-spohr
Arbeitskreis Wissenschaftliches Rechnen, 25.1.08
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AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Overview
1 Topics
2 Classical MD
3 Ab Initio MD
4 Systems
5 Coworkers
2/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Research Topics
Molecular Dynamics of Disordered Materials,Membranes, Electrolytes, Interfaces
with empirical (“classical”) force fields(hitnrun, GroMacs, Lammps )with reactive force fields; Empirical Valence Bondmodels (hitnrun)ab initio MD: Car-Parrinello, Born-Oppenheimer-MD(CPMD,CP2K)Mesoscopic Dynamics
Electronic Structure of Solids, Solid Surfaces,Adsorbates, Heterogeneous Catalysis(Crystal03, VASP)Monte Carlolattice models for fuel cell membranes, electrodes(hitnrun)
3/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Molecular DynamicsBasics
numerical integration of Newton’s equations of motion:performed stepwise tsim = Nstep · ττ � τchar tsim � τchar
=⇒ Nstep > 106 (better: > 108)almost all time (≥ 90 %) of an MD simulation is spenton calculating forcesforces are assumed to be pairwise additive: τ ∝ O(N2)
4/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Molecular DynamicsLong Range Forces
force truncation and neighbour tables (linked cell):−→ τ ∝ O(N)
long range forces: τ ∝ O(N2)
Ewald (lattice) sum: −→ τ ∝ O(N3/2)
PME, P3M (particle mesh ewald,particle-particle/particle-mesh): −→ τ ∝ O(N log N)
Fast Multipole Method (FMM) −→ τ ∝ O(N)
5/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Molecular DynamicsFor Large Systems
1. problem: large prefactors =⇒ parallelization viadomain decomposition2. problem: Nstep must be large =⇒ τ should be small3. problem: 2 synchronization steps (e.g. MPI) persimulation time step τ (one for forces, one forcoordinates) are necessary =⇒ τ � τnetwork
=⇒ Solution: many processors (small τ ) need to beconnected with a very fast network in order tosimulate long times for large systems. . . and that’s the problem!
6/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
ab initio MD
problems are similar as for classical MDτ is usually orders of magnitude larger! =⇒ It is ’easier’to use a large number of processors, provided thenetwork is fast enoughmake use of parallel linear algebra, FFT packages
7/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Polyelectrolyte Membranes
empirical (reactive)force fields
pore morphology
proton conductivity
proton mobility andtransportmechanisms inmodel pores
8/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Electrooxidation of C1 Compounds
DFT calculations ofadsorbate clusters
ab initio MD ofreactive processes
9/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Ab initio MDElectrocatalytic Oxidation of CH3OH to CH2O
10/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Oxygen Reduction on Perowskite Surfaces
ab initio/DFTcalculations
ab initiothermodynamics
=⇒ relative stabilities ofsurfaces
11/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Oxygen Reduction on LSM SurfacesSurface Models
12/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Oxygen Reduction on LSM SurfacesPhase Diagrams
∆µO / T / p
∆µLa
surface energy
∆µO / T / p∆µLa
13/14
AtomisticSimulations
Topics
Classical MD
Ab Initio MD
Systems
Coworkers
Acknowledgments
The GroupDr. Sergejs Piskunovs (AvH)
Dr. Klaus Kolster
Florian Wilhelm (Uni Ulm)
N.N.
External CooperationsDr. Sara Bonella, Prof. G. Ciccotti (La Sapienza, Roma)
Dr. Dmitrii Glukhov (in March), Prof. Renat Nazmutdinov (Kazan)
Prof. Wolfgang Schmickler (Ulm)
Dr. Timo Jacob (FHI Berlin, Ulm)
Dr. Christoph Hartnig (ZSW Ulm)
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