Performance improvements

Implemented update groups

Domain decomposition can now be based on so-called update groups. These are groups of atoms with dependencies during the update, which can be constraints and virtual sites. Update groups can typically be used when only bonds involving hydrogens are constrained and are enabled automatically when possible. This improves performance by eliminating MPI and OpenMP communication for constraints and virtual sites.

PME on GPU when running free energy perturbations not involving charges

PME can now be run on a GPU when doing free energy perturbations that do not involve perturbing charges.

PME long-ranged interaction GPU offload now available with OpenCL

On supported devices from all supported vendors (AMD, Intel, NVIDIA), it is now possible to offload PME tasks to the GPU using OpenCL. This works in the same way as the former CUDA offload. A single GPU can now be used to accelerate the computation of the long-ranged PME interactions. This feature means that only 2-4 CPU cores per GPU will be about as fast as the 2018 version that needed many more CPU cores to balance the GPU. Performance on hardware that had good balance of GPU and CPU also shows minor improvements, and the capacity for hardware with strong GPUs to run effective simulations is now greatly improved.

Intel integrated GPUs are now supported for GPU offload with OpenCL

On Intel CPUs with integrated GPUs, it is now possible to offload nonbonded tasks to the GPU the same way as offload is done to other GPU architectures. This can have performance benefits, in particular on modern desktop and mobile Intel CPUs this offload can give up to 20% higher simulation performance.