  The usefulness of solid-state spins in quantum technologies depends on how
long they can remain in a coherent superposition of quantum states. This
Colloquium discusses how first-principles simulations can predict spin dynamics
for different types of solid-state electron spins, helping design novel and
improved platforms for quantum computing, networking, and sensing.
  We begin by outlining the necessary concepts of the noise affecting generic
quantum systems. We then focus on recent advances in predicting spin-phonon
relaxation of the spin-defect qubits. Next, we discuss cluster methods as a
means of simulating quantum decoherence induced by spin-spin interactions,
emphasizing the critical role of validation in ensuring the accuracy of these
simulations. We highlight how validated cluster methods can be instrumental in
interpreting recent experimental results and, more importantly, predicting the
coherence properties of novel spin-based quantum platforms, guiding the
development of next-generation quantum technologies.
