ISU / DEC 10TH

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

InitialSimulations

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

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/hour NPAR 2 NPAR 4 NPAR 8 NPAR 16Regular 46.10/45.8* 57.845** 54.342 -Didn’t work

Gamma -- 60.277** 57.83 -Didn’t work

* Vasp 5.2.11** 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

Si9-O

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.