GBTOlib: a high-performance library for evaluation of molecular integrals

This is the first public release of the GBTOlib library. This library is used by the UKRmol+ codes but has a general applicability and has been written to allow interfacing with other codes.

Capabilities

• Evaluation of molecular integrals in the basis of atom-centered Gaussian orbitals and center-of-mass centered B-splines and/or Gaussians.

• The center-of-mass (i.e. continuum) basis can be built from either Gaussians, B-splines or a combination of the two.

• An arbitrary angular momentum for the continuum basis.

• Transformation of the atomic integrals into basis of molecular orbitals.

• Orbital orthogonalization using Gramm-Schmidt and/or Symmetric orthogonalization.

• Flexible configuration of the library allowing it to be ran on various machines ranging from single-node workstations to massively-parallel HPC architectures.

• Possibility to configure the library to use quadruple precision arithmetics and achieve higher than double precision of the actual integrals calculated.

• Input of molecular geometry, Gaussian basis and orbitals via the standard MOLDEN file.

Notes for version 3.0

• The main improvement in this version is the implementation of the MPI (distributed) evaluation of the mixed BTO/GTO integrals and the subsequent sparse integral transformation. In principle this allows to run arbitrarily large calculations using BTOs without an intermediate I/O only by increasing the total number of nodes (total memory) available for the calculation.
• In practice we have encountered some problems with very large calculations (even though the 32bit limitation of the MPI standard has been taken into account) but we deem those problems to be caused by limitations of the MPI libraries used rather than by GBTOlib itself.

Features added in this version:

• Implemented MPI evaluation of the mixed BTO/GTO integrals.
• Implemented MPI version of the sparse integral transformation.
• Renaming of the modules to ensure unique and uniform naming: all GBTOlib modules now carry the _gbl suffix.
• Optional calculation of exponentially damped dipole matrix elements implemented for all types of atomic integrals; new parameter in namelist process_control
• scatci_integrals now allows reuse of previously calculated AO/MO using basis_input in namelist process_control to indicate file path; allows sign-consistent calculations
• Molecular orbitals in the Molden format can now be written even if BTO basis is used (only GTO contribution considered); this is mostly useful in connection with UKRmol+ to write out the Dyson orbitals from calculations including BTOs.
• Backward compatibility with v1.0 integral files implemented
• scatci_integrals now exits early if integral file exists
• Verbosity control for GBTOlib implemented and keyword added to redirect output to terminal
• Some keywords added to documentation
• Some improvements to memory allocation
• Changes to what is/is not printed by default: different verbosity levels (1-4) can now be selected using the 'verbosity' flag in the namelist process_control for scatci_integrals.
• Change of intent of some variables; avoids compiler warning when compiling with Intel Fortran 2020
• Minimal basis test for H2 added
• Bugs corrected:
  • to prevent memory leak in free_scattering_gbl module
  • accurate memory allocation in routine eval_CGTO_shell_pair_pw_expansion to avoid invalid memory acces
  • to avoid integer overflow (in routine eval_boys) in LP64 mode
  • so evaluation of amplitudes for irreducible representations without orbitals is skipped
  • in integrals_D2h_photoionization_CC_parallel test when 32-bit MPI library is used
  • when writing of a MOLDEN file when equivalent atoms are presentand when the order of the atoms does not match the order of the centers of the GTOs in the basis.