[CP2K-user] [CP2K:16945] Ar Basis sets

[Matthew Graneri]

Hi there,

I was wondering if I could get some advice/help on running an AIMD 
calculation to run? I've *no* experience with AIMD, MD, or any plane wave 
calculations (my only experience is with ab initio methods in ORCA and 
Gaussian), and no one else in my department has any experience with AIMD 
calculations, either... I've finally gotten to the stage where I can start 
an AIMD calculation (it's taken weeks to get to this stage!), but I have 
come across a persistent issue which I do not have the expertise to solve.

Essentially, I want to simulate my molecular system in a solid argon 
matrix, and calculate IR spectra to compare with experiment. So far, I've 
optimised my cutoff/rel_cutoff values, gotten my input files sorted, gotten 
CP2K installed installed on our local HPC, and tested that it works for a 
few of the test systems provided for the IR/RAMAN and HFX tutorials.

Based on results from a recent study, I want to use B3LYP with a double 
zeta basis set, which I am very well aware will take a long time to 
complete... According to the CP2K website (and my own testing), it looks 
like using either the ADMM or RI approximations might speed up this 
calculation to a rate which will be acceptable for our HPC. The problem is 
that I cannot find any *matching* primary, potential and auxiliary basis 
sets for argon. In fact, I cannot find any auxiliary basis sets for argon 
at all.

Is this because argon doesn't require an aux basis set for RI or ADMM? Does 
anyone know of any basis set families which I could use for my 
calculations? They'd need to be of at least double zeta quality, and 
include basis sets for H, C, N, S and Ar.

Also, three unrelated questions (but things which I've been confused/unsure 
about when trying to learn all this stuff):

   1. what's the difference between the 'global' and 'massive' thermostats? 
   The academic (yes, there's only one) at my university who has experience 
   with MD had never seen those terms before, so I'm not sure how they differ.
   2. Are the cutoff/rel_cutoff values basis set dependent? As in, if I 
   swap the basis sets I ran my testing on based on advice I get here, would I 
   need to rerun my testing for the new basis set, or could I use the values I 
   determined using the original basis sets?
   3. Are there any 'rules of thumb' as to how big a cell should be used 
   for a system like mine? Essentially, I've embedded my molecule in a crystal 
   of argon. I'm *not* trying to extrapolate this to a larger crystal 
   structure (I think that means it's 'non periodic'?)

I'd really appreciate any help I can get with this; I'm very much out of my 
depth here...

Thanks in advance!

Matthew~

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