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

eckhard.spohr@uni-due.dehttp://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

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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)

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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)

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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)

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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!

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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

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AtomisticSimulations

Topics

Classical MD

Ab Initio MD

Systems

Coworkers

Polyelectrolyte Membranes

empirical (reactive)force fields

pore morphology

proton conductivity

proton mobility andtransportmechanisms inmodel pores

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AtomisticSimulations

Topics

Classical MD

Ab Initio MD

Systems

Coworkers

Electrooxidation of C1 Compounds

DFT calculations ofadsorbate clusters

ab initio MD ofreactive processes

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AtomisticSimulations

Topics

Classical MD

Ab Initio MD

Systems

Coworkers

Ab initio MDElectrocatalytic Oxidation of CH3OH to CH2O

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AtomisticSimulations

Topics

Classical MD

Ab Initio MD

Systems

Coworkers

Oxygen Reduction on Perowskite Surfaces

ab initio/DFTcalculations

ab initiothermodynamics

=⇒ relative stabilities ofsurfaces

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AtomisticSimulations

Topics

Classical MD

Ab Initio MD

Systems

Coworkers

Oxygen Reduction on LSM SurfacesSurface Models

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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

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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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