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

Using VASP Available VASP versions : 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

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

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! Step/hourNPAR 2NPAR 4NPAR 8NPAR 16 Regular46.10/45.8*57.845** Didn’t work Gamma **57.83-Didn’t work * Vasp ** The simulation didn’t finish.

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.

Si9 - O

Temperature response

Si-9 Energy

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.