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ISU / Dec 10 th

ISU / Dec 10 th. Joaquin Peralta, Rupa Dumpala , and Scott Broderick. First simulations / QE. Quantum espresso Convergence parameters Technical Issues Undefined ‘ input_file ’ to add initial velocities. Defining by modifying source code. Alternatives VASP/QE Coding. Initial Simulations.

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ISU / Dec 10 th

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  1. ISU / Dec 10th Joaquin Peralta, RupaDumpala, and Scott Broderick

  2. First simulations / QE • Quantum espresso • Convergence parameters • Technical Issues • Undefined ‘input_file’ to add initial velocities. • Defining by modifying source code. • Alternatives VASP/QE Coding Initial Simulations

  3. Using VASP • Available VASP versions : 5.3.2 and 4.X • Pseudo potentials • PAW – PBE/LDA • Alternative of request all-electron (very small number of atoms) • Convergence settings • Molecules with considerable vacuum space • Plane Waves must be around 50% more than the used in classical crystalline structures (RAM memory) • Partial occupancies (smearing). In particular for the case of molecules and DM, Fermi-smearing or Gaussian-smearing will be used. • Compilation Issues • Performance • Gamma Point

  4. Si9 Cluster • Original Adri’s group Si cluster of 9 atoms. • Reducing vacuum space size to improve convergence and plane waves. • A cubic cell of 30A it was the first option. • Silicon first because : • Performance Input : ISPIN / ENCUT / NGX • Performance Compiling : Gamma Point / Settings • Vacuum Space, Plane waves and Memory requirements

  5. Si9 / Cluster • Trying to fit best parameters for simulation time • Technical issues with • Cluster platform fails with NPAR major than eight • Compiled version don’t run with a wrong number of NGX, NGY, and NGZ • Not considerable performance improvement with more aggressive compilation • 1 Ionic step/minute  1fs each step  5ps = 83 hours • 1 Ionic step/minute  0.25fs  5ps = 13 days! * Vasp 5.2.11** The simulation didn’t finish.

  6. Si9 - O • Incorporation of Oxygen in the system • Using ISMEAR Associated to the temperature of the input file from Adri’s group. T = 338 K • Oxygen ENCUT increased the time of the RUN. • Technical initial problems / Times • Using 64 CPU / NPAR 4  Work ~1 step/min. • Using 64 CPU / NPAR 8  Faster, but suddenly simulation stop. • Using 128 and 256 CPU • NPAR > 8  Simulation faster ~ 1.5 to 2.0 step/min • Principal problem, after a couple of hours the simulation stop for different problems • Zombie process (Cluster environment problem) • Setup ENCUT / NGX / etc.

  7. Si9 - O

  8. Si9-O

  9. Si9-O • Temperature response

  10. Si-9 • Energy

  11. Next steps • Reduce vacuum space to improve simulation times. • Reduce compiling optimization and disk I/O • Cluster problem(s) • FFT size grid  Better accuracy, slower simulation time. • Based on old NPAR and CPU studies to compare.

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