SPADE 1.0: A Simulation Package for Non-Adiabatic Dynamics in Extended Systems

Nonadiabatic molecular dynamics (NAMD) simulations are crucial for revealing the underlying mechanisms of photochemical and photophysical processes. Typical NAMD simulation software packages rely on on-the-fly <i>ab initio</i> electronic structure and nonadiabatic coupling calculations, and thus become challenging when dealing with large complex systems. We here introduce a new Simulation Package for non-Adiabatic Dynamics in Extended systems (SPADE), which is designed to address the limitations of traditional surface hopping methods in dealing with these problems. By design, SPADE enables the users to define arbitrary quasi-diabatic Hamiltonians through parametrized functions and incorporates a variety of algorithms (e.g., global flux hopping probabilities, complex crossing and decoherence corrections), which can realize efficient and reliable NAMD simulations without using nonadiabatic couplings at all. All the employed methods and expressions for diabatic Hamiltonian matrix elements can be flexibly set through the input files. SPADE is mainly written in Fortran based on a modular design and has a great capacity for further implementation of new methods. SPADE can be used to simulate both model and atomistic systems as long as proper Hamiltonians are provided. As demonstrations, a series of representative models are studied to show the main features and capabilities.