sPuReMD: add QMMM library interface for external codes (e.g., Amber). Rework file I/O parsing to jive with multiple consecutive simulation code changes. Improve file parser error checking (numeric types). Other code clean-up.

sPuReMD: fixes for multiple consecutive simulation codepath. Reorganization to this codepath (some data structure now carry a flag to designation their allocation state). Fix bug in force field parser (atom type not truncated correctly). Charge sparse_matrix structs to be non-pointers to jive with new allocation state flag. Other code clean-up.

sPuReMD: finalize sPuReMD multiple consecutive simulation code (for integration with other codebases).

PG-PuReMD: fixes to NVT with Berendsen thermostat. Use updated constants from sPuReMD. Add BGF geometry file parser. Other code clean-up.

sPuReMD: fix memory leak with ICHOLT preconditioner (droptol for OpenMP only) for charge solver. Default to Jacobi preconditioner. Resolve several compiler warnings around C strings (snprintf, etc.). Other code clean-up.

sPuReMD: add functionality to run multiple MD simulations (for usage via integration with external codebases).

sPuReMD: resolve OpenMP build errors with GCC v10 (behavior changes for function arguments). Suppress possibly unitialized variable warnings for BiCGStab.

sPuReMD: finalize corrections for pressure calculations. Change output units from GPa to ATMs. Other formatting changes.

PG-PuReMD: merge changes from sPuReMD and PuReMD for validation work for simulation accuracy. Small correction to lone pair energy calculation. PuReMD: code formatting changes to better align with sPuReMD. sPuReMD: fix issue with valence angle calculations not setting list indices under certain sitations (taking previous continue statement missed index assignment).

PuReMD: backport changes for interaction function calculations. sPuReMD: alignment with PuReMD code.

sPuReMD: output PDB files according to write_freq value in control file in addition to outputting to the trajectory file. Small tweak to PDB output format to be in compliance with specification.

sPuReMD: fix issue with runs using restart files overwriting velocities to zero. Change behavor to warn if conflicting conditions exist for generating initial atom velocities. Revert formatting change of pressure logs. Enable pressure file logging when compute_pressure = 1.

sPuReMD: add control file parameter to compute atomic system pressure for non-NPT ensembles. Fix issues with isotropic NPT ensemble (incorrect pressure and temperature scalers). Change atomic position remapping behavior to include upper boundaries of the simulation box (shared memory code only). Other code clean-up.

sPuReMD: replace OpenMP critical sections on ext_press with thread-local storage and subsequent reduction (ext_press_local). Other code clean-up.

sPuReMD: corrections to external pressure calculations for NPT-type ensemble simulations (use correct periodic images between reneighboring steps). Other code clean-up.

sPuReMD: fix issue with torsion & conjugation forces being incorrect due to rel_box arithmetic being wrong (incorrect directions for position vectors). Redesign atomic distance and position update functions to support both periodic boundary conditions and non-periodic boundary conditions.  Behavior change: let random_velocity parameter in control file take precedent over specifying a non-zero initial temperature value. Other code clean-up.

sPuReMD: disable debug prints (DEBUG -> DEBUG_FOCUS). Small tweaks to valence angle code to better match reference. Other code clean-up.

sPuReMD: refine BiCGStab implementation to not falsely report numeric breakdown. TODO: decide on correct checks for level of precision in numeric breakdown checks.

sPuReMD: add support for using the Tensorflow machine learning library to prediction initial guesses for the charge solver using the long short-term memory model (LSTM) via frozen models in GraphDef files.