single atom alloy surface builder

[ikowalec]

To speed up the creation of SAA slabs and to keep them tidy.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0e90a5d) 86.49% compared to head (e114789) 86.58%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #137 +/- ## ========================================== + Coverage 86.49% 86.58% +0.08% ========================================== Files 72 72 Lines 2829 2847 +18 ========================================== + Hits 2447 2465 +18 Misses 382 382 ``` | [Flag](https://app.codecov.io/gh/logsdail/carmm/pull/137/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Logsdail) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/logsdail/carmm/pull/137/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Logsdail) | `86.58% <100.00%> (+0.08%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Logsdail#carryforward-flags-in-the-pull-request-comment) to find out more.

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[OscarvanVuren]

Line 136 - SSA instead of SAA? Is it substituted single atom (SSA) alloy or substituted single atom alloy (SAA)? Or SSSA? Otherwise this looks alright to me.

[ikowalec]

Line 136 - SSA instead of SAA? Is it substituted single atom (SSA) alloy or substituted single atom alloy (SAA)? Or SSSA? Otherwise this looks alright to me.

Thanks for spotting, I do not know why I am so fixated on SSA.