How to get the directives of a slurm for my Quantum ESPRESSO calculations?

Question

Context

I saw some examples of SLURM scripts on the internet like the one below:

#!/bin/bash
#SBATCH -J QE68
#SBATCH --ntasks=16
#SBATCH --ntasks-per-core=1
#SBATCH --partition=defq
#SBATCH -o %x-%j.out
#SBATCH -e %x-%j.err

Problem

I am having a hard time understanding the specific values that are initialized to the various directives. For example, ntasks=16 and ntasks-per-cor=1.

How can I know in prior that ntasks=16 not 17, why ntasks-per-cor=1 and not 2?

I don't know how to arrive at those numbers, or which commands I should use to get them before constructing a SLURM script.

Question(s):

1. How can I determine what numbers I need to use for the various directives?

2. Are there any good rules of thumb to determine these numbers?

Answer 1

Since the question was edited, here is an updated answer.

1. How to estimate the numbers which we initialize the SLURM directives:

As far as I understand, the way to decide the numbers that you initialise the SLURM directives are by empirical means.

So one way to estimate those numbers are by running your script on a very small subset on your local PC and logging various specifications of your PC. This could help you to calculate how long, how much memory you might need for a larger population (more molecules, more stronger basis sets etc).

For example, if you run a CCSD_T calculation for 1 molecule containing 20 atoms on your local PC. And suppose it takes 14 mins on your local PC which has 32 GB RAM, 6 cores.

So if you wanted to run the calculations for 100 such molecules on the supercomputer, with 32GB RAM and 6 cores, you can estimate that it would take 100*14 = 1400 mins, which is about 23 hours !

So perhaps you would want to increase the RAM to 64GB or maybe 128GB. Which would mostly half and quarter your time. So maybe at 128GB it would take 6 hours.

So in that way you can say:

#SBATCH --time=6:00:00
#SBATCH --cpus-per-task=6
#SBATCH --mem=128000

2. Good rules of thumb for determining the values for SLURM directives:

For the --mem= directive, use values which are powers of 2.

---

To Print out what values are initialized when you run the shell script

You can access the various parameters using the SLURM environment variables. A complete list of the environment variables are found on the SLURM webpage.

input-environment-variables

output-environment-variables

Here is an example of how to print information regarding these parameters using SLURM environment variables:

Say we have a test.sh with the following contents:

#!/bin/bash
#SBATCH -J QE68
#SBATCH --ntasks=16
#SBATCH --ntasks-per-core=1
#SBATCH --partition=defq
#SBATCH --mem=800
#SBATCH -o %x-%j.out
#SBATCH -e %x-%j.err
printf "N tasks per core %s\n" "$SLURM_NTASKS_PER_CORE"
printf "Number of tasks  %s\n" "$SLURM_NTASKS"
printf "Memory per node  %s\n" "$SLURM_MEM_PER_NODE"

Upon scheduling this sh script with: sbatch test.sh

In the output file, we would see the following output:

N tasks per core 1
Number of tasks  16
Memory per node  800

Answer 2

The SLURM general directives are given on the SLURM webpage, as indicated in the other comments.

The Digital Research Alliance of Canada uses the script below to launch QuantumEspresso jobs:

#!/bin/bash
#SBATCH --account=def-someuser
#SBATCH --time=0-1:00           # DD-HH:MM
#SBATCH --nodes=1
#SBATCH --tasks-per-node=32     # MPI tasks
#SBATCH --mem=0                 # all memory on node
module load StdEnv/2020  intel/2020.1.217  openmpi/4.0.3
module load quantumespresso/6.6
srun pw.x < si.scf.in > si.scf.out

There are no specific directives for specific software.