Release of MidasCpp 2026.10.0

We are happy to announce the new MidasCpp 2026.10.0 release. Just follow the instruction in the manual or directly go to our GitLab page to clone the git repository or to download the source code.

New Features

Added #3 EmbSys under #2 Vcc for doing embedding VCC calculations, currently only supported by the VCC[2H2] method.
Subsystems may be frozen in the VCC part (modal basis limited to 1) using #3 FreezeEmbsys, also under #2 Vcc.
Added #4 EmbReducedTransform under #3 Rsp for solving the embedding VCC eigenvalue problem approximately
by transforming the full problem using 0th order (uncoupled) trial vectors. This keyword takes the options
OFF, ONLYA and INCLUDEF.
Added #4 AnalysisEigenVectorElems under #3 Rsp, allowing users to choose the number elements to show
in the eigenvector analysis.
Added #3 WriteIncrInputFromFile as an alternative to #3 WriteIncrInput for DIF(ACT) calculations, which takes a file name as its argument.
In that file, fragments and fragment combinations can be predefined, as well as coefficients for the fragment combinations.
If only fragments/fragment combinations are predefined, coefficients are calculated as before.
If coefficients are also predefined, those will be used.
Using option --print, test/TEST will now print the test names that would be run and exit.

Changes

Rewrote a term which was causing the twomode RJac transformer to have M^4 scaling as opposed to the theoretical M^3.
Fixed an issue where the zeroth order Jacobian for the twomode and old VCC transformers defaulted to subtracting
the VCC energy as opposed to the VSCF energy on the diagonal, causing poor convergence for large systems.
Added the option to use the VCC energy (analogous to how it was before) by using the #4 ADiagVccRefEnergy keyword
under #3 Rsp.

Bugfixes

Fixed an issue where running an MPI calculation using a .v3c-file that was not already present,
could result in a race condition where some MPI ranks would be reading the file
while others were trying to write it.
Fixed a small issue in the VccInput module, where for some niche calculations the program could crash.
Fixed a bug which caused twomode LJac transformations to be incorrect in cases where the
mode combination range of the operator and wave function differed.
Fixed an issue where VCC left- and right Jacobian eigenvectors were not being properly biorthogonalized
in cases with degenerate excitations, causing these to have incorrect transition strengths.
Fixed an issue in the iterative solver, where the preconditioner in some cases could become singular and produce NaN results.

Let us know if you encounter any problems.

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