Lets approve this request, and make the time good through the end of Q2. Ray On 9/4/13 4:01 PM, "[email protected]" <[email protected]> wrote:

Hello,

A yearly allocation for the LCRC cluster has been requested with the following updated information:

Submitter/PI: John Russell Project Name: lith_ox_md Division: MSD Project title: Molecular Dynamics Calculations of Lithium Oxides Associated funding: Strategic LDRD project entitled Multiscale Modeling of Advanced Electrical Energy Storage Systems Other Systems: Carbon, CNM Science: We will perform molecular dynamics (MD) simulations on nanocrystalline lithium-oxide compounds (including Li2O and Li2O2) of relevance to lithium-air batteries. These simulations include determination of the structures, energies and some properties (such as the diffusivities) of the free surfaces and grain boundaries in these microstructures. A key feature of the simulation approach involves the use of a method to evaluate the Coulomb energy, forces and stresses by direct 1/r summation with spherical truncation (Wolf et al. 1999). This order-N method, which has recently been incorporated into the LAMMPS code that will be used for this work, is computationally superior to both the widely used Ewald method and fast-multipole methods while at the same time producing numerically identical and physically more transparent results. Using this approach, we are able to consider ionic systems consisting of a very large number of ions, thus enabling elucidation of microstructu ral phenomena and physical behavior that can subsequently be used as input to parameterize a physically realistic mesoscale battery model of microstructure evolution during the charge/discharge cycle. Project description: The goal of this project is calculate structural and thermodynamic properties of lithium-oxide materials and to develop parameters for collaborators studying mesoscale models where experimental values may be unavailable. Our initial approach will be to use a Buckingham potential to model covalent interactions and a Wolf summation potential for elecrostatic interactions in a fixed charge Li2O model as implemented in the LAMMPS molecular dynamics package. Our model systems will include free particles, surfaces and nanocrystalline materials. This modeling approach is well suited for large systems due to the favorable scaling of the potentials and software. LAMMPS is massively parallel with nearly linear scaling with system size which can allow for 100k+ atom models for tens of nanoseconds.

We are also developing a variable charge lithium-oxide molecular dynamics potential suitable for modeling lithium superoxide, lithium peroxide, and Li2O. The computational cost of this method is estimated as 25x as expensive as a Buckingham pair potential, but with much greater flexibility to model different lithium-oxide stoichiometries. Project URL: Current FY Hours Used: undetermined amount

New FY Requested allocation: 500000 Q1: 125000 Q2: 125000 Q3: 125000 Q4: 125000

Justification: LAMMPS is a linear scaling molecular dynamics code. We will be using the Wolf summation potential to model electrostatics, which is very important due to the fact that FFT methods for electrostatics such as PPPM and PME are NlogN scaling.

The Wolf summation is directly incoporated into our variable charge model. The variable charge itself has costs due to charge equilibration, which should put it on par with MEAM and AIREBO. In LAMMPS these methods are compared to a Lennard-Jones (LJ) potential as a benchmark reference (LJ = 1.0, Buckingham ~ 1.0). MEAM is rated at 16.5x and AIREBO at 40.6x. This is primarily due to loops over second nearest neighbors. Therefore, we expect the potential to be in the range of 25x scaling.

Thank You,

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