Efficient simulation of periodic problems in NMR. Application to decoupling and rotational resonance

A numerical algorithm is described for efficient calculation of the dynamics of nuclear spin systems under a periodic Hamiltonian, The method employs time-domain integration of the quantum evolution over a single modulation period. This information is used to construct the NMR spectrum, effectively with infinite frequency resolution. The computation procedure is more rapid than Floquet simulations in the frequency domain and explicit calculation over long times in the time domain. Furthermore, it avoids the ambiguity in the eigenvalues associated with the effective Hamiltonian approach. The method is demonstrated by calculating the NMR spectrum in two different circumstances: (i) heteronuclear spin decoupling by periodic radiofrequency irradiation, and (ii) recoupling of homonuclear dipolar interactions in rotating solids by spinning at the rotational-resonance condition. (C) 1996 Academic Press, Inc.