Open Boundary Conditions and Implicit Solvation Calculations in CASTEP using DL MG

CASTEP is a quantum mechanics simulation code specialised for solid materials and is heavily used on ARCHER2 (~50 users per month). CASTEP’s support for obtaining the ground-state electronic and atomic configurations is very good for solid materials with , periodic (repeated) crystal structures. There are a wide range of materials science, chemical and biological applications for which it is desirable to compute the properties of isolated molecules or molecules in solvent, e.g. energy storage or drug development. In an eCSE project carried out under the previous ARCHER service (eCSE07-006), the periodic approach of CASTEP was extended to enable simulations in Open Boundary Conditions (OBCs) and in the presence of a solvent, by adopting the minimal-parameter solvent model already developed in ONETEP, another materials modeling code.

This poster presents the work that was achieved in ARCHER2-eCSE01-09 which extended the OBC/solvation functionality in CASTEP to address the limitations of the original implementation:

• Calculation of the ionic forces was implemented, allowing dynamical simulations of molecules in OBCs/solvation, massively extending the utility of the functionality.
• The position of the solvent can now be updated self-consistently with electronic state of the system, which is a far more accurate model of molecules in solvent.
• The solution to the OBCs Poisson equation is now computed using additional levels of parallelism. This improves the performance of the code at the most computationally intensive step of the calculation (7x speed up on a sample calculation), reducing the Time:Science ratio for these calculations.