Projection of fixed atoms out of Hessian in L-ANCOPT and FIRE optimizers

[clavigne]

This PR fixes #410.

I've tested that it works using this xcontrol file for FIRE and this one for L-ANCOPT, with this initial geometry.

Running L-ANCOPT prior to the fix yields this final geometry

3
xtb: 6.4.0 (d4b70c2b361067f291e81c3df1d1c31c28d01cb4)
H        -0.79575145519344    0.12524065205080   -0.00000000099274
H         0.96541707812111    0.14678380837277   -0.00000000237865
O         0.03033437297265    0.72797553581838    0.00000000000000

After this PR, running the same optimization yields

3
xtb: 6.4.0 (d4b70c2b361067f291e81c3df1d1c31c28d01cb4)
H        -0.77226423724448    0.14366978476487    0.00000000477125
H         0.97226467309956    0.14366934440933   -0.00000000941527
O         0.01526020355893    0.62582966774369    0.00000000000000

which has the correct coordinates for the first first two atoms. For FIRE, the projection is only involved when the optimization is preconditioned, which is currently not a setable option. However, I hand-set it to obtain the following pre-PR optimization result

3
xtb: 6.4.0 (d4b70c2b361067f291e81c3df1d1c31c28d01cb4)
H        -0.63257492583150    0.05605455560180    0.00000000000000
H         1.20029965304500   -0.14298093394565   -0.00000000000000
O         0.33157878141598    0.39598095953997    0.00000000000000

and post-PR,

3
xtb: 6.4.0 (d4b70c2b361067f291e81c3df1d1c31c28d01cb4)
H        -0.77226423661793    0.14366978520871   -0.00000000000000
H         0.97226467499076    0.14366934683588   -0.00000000000000
O         0.10047054653320    0.62475919881618   -0.00000000000000

The important part is that in either cases the pre-PR includes significant displacement of the fixed atoms, due to the lack of Hessian projection. This is now fixed.

[codecov]

Codecov Report

Merging #433 (8752196) into master (d4b70c2) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #433      +/-   ##
==========================================
- Coverage   40.80%   40.79%   -0.02%     
==========================================
  Files         304      304              
  Lines       50774    50787      +13     
==========================================
  Hits        20718    20718              
- Misses      30056    30069      +13     

Impacted Files	Coverage Δ
src/relaxation_engine.f90	0.00% <0.00%> (ø)

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[awvwgk]

Thanks for sharing.