Simulation of a Free Induction Decay

In NMR-SIM the simulation of an NMR experiment is based on the density matrix approach with relaxation phenomena implemented using a simple model based on the Bloch equations. Spectrometer related difficulties such as magnetic field inhomogenity, acoustic ringing, radiation damping or statistical noise cannot be calculated using the present approach. Similarly neither can some spin system effects such as cross-relaxation and spin diffusion can be simulated. 

The FID is calculated from the solution of the Liouville-von Neumann equation, which is often called the density operator equation, and which describes the dynamics of quantum mechanical systems. 

Load the configuration file ch3221.cfg (File I Experiment Setup Load from file...)- Open the NMR-Sim settings dialog box (Options I NMR-Sim settings...) and select the option Relaxation Acquisition. Run the simulation (Go I Run experiment). Apply an exponential window function (Window button) but no DC correction. Fourier transform the FID (FT button). (The effects of window functions are explained in section 3.2.3). Save the spectrum (FilelSave) for comparison with the second calculation. For the second simulation select the option Relaxation None and run the simulation saving the file with a new name. Process the data in exactly the same way as for the first simulation (Window and then the FT button) and compare the two spectra using the dual display mode of 1D WIN-NMR (DisplayIDual Display) (see section 3.2.3.4). 

The gyromagnetic ratio of a nucleus influences both the resonance frequency and, more importantly for NMR-SIM simulations, the rf pulse lengths. The resonance frequency of a nucleus is a function of its gyromagnetic ratio and is related to the basic IR frequency of the spectrometer as shown in equation [3-6]. The gyromagnetic ratio of the excited nucleus effects both the rf power and the pulse length, equations [3-7] and [3- 

Consequently NMR-SIM has the option to modify the rf pulse behaviour according nucleus being excited and to generate spectra that are close to real experiments. 

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