Hi, I want to clarify a few of the things about the usage of g_rotacf (for rotational correlation function for molecules). In the manual it is given like the following:
g_rotacf -P 1 -nparm 2 -fft -n index -o rotacf-x-P1 -fa expfit-x-P1 -beginfit 2.5 -endfit 20.0 I understood that -f, -s options are needed to be included in the above list. It is mentioned in the manual, that the above command will calculate the rotational function using a first order Legendre polynomial of the angle of a vector defined by the index file. (as I understand, -P 1 option is taking care of this. If I want to use the second order Legendre polynomials, -P 2 will do it for me I suppose) The above command will also fit the calculated correlation function to a two parameter exponential (-nparm 2 is taking care of this I suppose). Does it mean that the calculated correlation function is expressed as a sum of three exponential terms with two variables along two directions ? What is the fit function by default is used here ? Is it exp(-l(l+1)Di) ? There is also an option -fitfn in the list, what are these functions are meant for ? -fft option is for using FFT for the computation of the correlation function if I am correct. -fa option I dont have any idea about it. Thanks and Regards in advance, Ram.
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