Atomic calculations

kajackson's picture
Submitted by kajackson on Thu, 12/01/2016 - 18:42

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We are running a systematic series of calculations to find the lowest-energy arrangements of the Fermi-orbital descriptors (FOD's) for the atoms from H to Kr. The calculations involve extensive searches for the optimal arrangements, starting from a large number of different random starting arrangements, which are then relaxed to a local minimum energy arrangement using the conjugate gradient (CG) method. Through tests on the Cr atom, we find that doing the CG optimizations while keeping the occupied orbital space frozen gets us very near to the final optimized FOD positions where the occupied orbital space is also optimized via SCF calculations. More details of this method in a future post.

jkortus

Tue, 01/03/2017 - 04:07

We used guesses for the FOD's based on "chemical intuition" and we already have reasonable well converged results for the (free) Atoms:

H, He, Li, Be, C, Ne,
Na, Mg, Al, Ar
K, Ca, Sc, Mn(?), Zn, Kr

We started with guesses based on shell structures:

1s -> core position
2s2p -> tetraeder(s)
3s2p -> tetraeder(s)

for elements were d-electrons get involved we were partly successful by using a 10-edge body as starting configuration (two 5-rings, alternated placement of SUP and SDN FOD's).
It works reasonable well if one restricts the movement of the FOD's to shells, meaning for example one can modify the optimization algorithm to only optimize the position between a given dR from the core.

A further problem is, that for closed shell systems (full rotation symmetry: Ne, Ar, Kr) the tetraeders for SUP and SDN can be freely rotated with respect to each other without changing the SIC energy.

Question: What may be the "correct" solution:

1) SUP and SDN positions 'paired'
2) SUD and SDN to maximize the 'gap' between them (electron repulsion ?)

Best,
Torsten.

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admin

Thu, 09/21/2017 - 15:51

As per Dr. Jackson, here is an attachment, please remove the .txt attachment to extract after downloading it. This is a security feature from the system.

file: 
Plain text icon TESTS.tar_.txt

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