Mathematics
The hamiltonian we use for NMR systems is of the form
with gyromagnetic factors , chemical shifts of nuclear spin , coupling between spins and denoted as , and , with being the usual spin operators.
Within NMR, we have a strong magnetic field in the -direction, and electromagnetic pulses / oscillating fields are applied to flip the spins into the plane. Since typically is of the order of 500Mhz, the pulses of 10kHz bandwidth, and the required resolution is sub 1Hz, we refrain from modeling the explicit time dependence of the pulses. Instead, we model the pulses directly by calculating the spectral function, i.e., time-dependent correlations between the corresponding operators.
The spectrum measured in an NMR experiment corresponds to the spectral function, which is the Fourier transform of the correlation function of the operators , calculated by the quantum program created by the HQS Qorrelator App.
Calculation of the spectral function
The spectral function of the NMR problem is given by the Fourier transform
where the operators, , contain the gyromagnetic factors for convenience, and is the real time dependence.
The contribution of an individual nuclear spin to the full NMR spectrum is obtained via
while the full NMR signal is the sum of individual contributions.