[Wien] How much computer CPU usage will be required for say a 60 atom model to run. So we want CPU requirements versus the number of atoms for Wein2k

[Peter Blaha]

Hi,

This question is not so easy to answer, since it is not so clear what 
kind of HPC you would "rent" (But even 2000 hours is "very little/nearly 
nothing").

A 60 atom cell (with "complicated atoms, LDA+U, ...") can still be run 
on a modern PC with 8 cores and 64 (better 128) GB RAM. A single scf 
calculation may take 1-10 h on this PC.

Of course such calculations run faster, when you couple a few PCs (or 
nodes on a HPC) together and let them work in parallel.

Much more difficult is to estimate how many such scf cycles you will 
have to run. This depends a lot on your skills and what you actually 
want to calculate. Certainly, phase transitions, entropy, ... require 
MANY such calculations (100 to a few 1000 ?). There is no "input switch: 
"Phase transition" or "entropy", you have to set up models, calculate 
them and derive from the results (total energies) your information. It 
requires quite some expertise !

I don't know what they would charge you for 2000 h on a HPC cluster, but 
this is just the cpu time you get from a single PC (costs 2000 US$) in 3 
month. Unless you get "very good prices" (nearly for free), renting CPU 
hours is usually quite expensive as compared to buying your own small 
cluster, in particular when you go with standard PCs and not with a rack 
solution based on Xeon processors.

The drawback is, that you need to be able to administer the Linux 
installation (including network and NFS setup, ...)

For this project, I'd probably buy 4 - 8 PCs (or more, I don't know how 
much money you have) (latest Intel I7 or I9 processors (or whatever the 
numbers are now) with 8 cores, 128 GB RAM) and a good Gbit switch 
(unless your University provides a good network anyway). Such a cluster 
can then run for a couple of years (at least the life of a PhD student) 
providing you with more than 100000 cpu-h.

HPC systems really are needed only if you go to systems with more than 
100-500 atoms/cell, where one MUST use highly parallel mpi jobs, which 
need several nodes and a Infiniband network. It is a waist of HPC 
ressources, when you use just one node of such a cluster. A single node 
on a HPC system is NOT faster than a modern PC !!!

Hope this helps.

Peter Blaha

Am 10.02.2022 um 10:22 schrieb Mohammed S. Mohammed:
> _<#_msocom_1>Dear Wien2kMailing list users
> In Egypt we are about to invest some money from a project fund to *Buy 
> or Rent *a high performance computer to calculate the magnetic, 
> electronic, elastic, and magnetocaloricproperties of selected 
> rare-earth transition metal compounds to include R_2 Fe_14 B, Nd_3 
> Co_11 B_4 .The problem is we have to state in our request for this 
> fund how much computerCPU usage will be required for say a 60-atom 
> model to run. Therefore, we wantCPU requirements versus the number of 
> atoms for Wein2k. Also need to estimatehow many times these models 
> will need to be executed to perform the field,temperature ranges, 
> first and second order phase transitions, magnetization, specificheat, 
> entropy, and MCE properties i.e. the isothermal change in entropy and 
> theadiabatic change in temperature in a wide range of magnetic fields 
> and in atemperature range up to the Curie temperature of the studied 
> systems.
>
> I am not sure that we can estimate the number of flops; so far, I have 
> not seen this type of information on the internet for wien2k. There 
> are tools, but not clear, if there has been a paper on the subject. 
> The issue I see is that we need to estimate how much computer time to 
> ask for, so if we can get an estimate that would be a good idea. If 
> they give us, 200 or 2000 hours will that, be enough to do what we 
> want? How much computer time/gflops do we ask for?
>
> Thank you foryour patience.
>
> Dr / Mohammed Said M. Abu-Elmagd
>
> Ph.D. in TheoreticalPhysics /Department of//Physics, Higher Institute 
> of Engineering, Shourok Academy, Cairo, Egypt./
>
>
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email:peter.blaha at tuwien.ac.at           
WWW:http://www.imc.tuwien.ac.at       WIEN2k:http://www.wien2k.at
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