qdmag: A Python package for simulating the time-dependent magnetization using quantum master equations

We present qdmag, a computational utility for calculating the magnetization of magnetic molecules under a varying external magnetic field by solving a generalized quantum master equation. The package relies on the spin Hamiltonian formalism, which includes both the magnetic exchange interaction and the zero-field splitting (ZFS) interaction. Different types of magnetic exchange interaction and ZFS terms up to 12^th order, which are written in terms of the extended Stevens operators, are supported. qdmag enables long-time evolution of magnetization for up to a few milliseconds, which is achieved through a staircase approximation of the magnetic field as a function of time. For high-dimensional spin Hamiltonians, a lower-dimensional effective Hamiltonian is constructed to make the calculations computationally feasible. Three case studies of a monomer, a dimer, and a trimer are presented to demonstrate the use of qdmag. Our work offers a computational tool to bridge the gap between theoretical development and numerical calculations of spin dynamics in the presence of spin-phonon coupling.