Hi Eva,
The 'ttm gauss f1 f2' option in CONTROL specifies part of an electronic energy deposition (for laser irradiation) in the Two-Temperature Model (TTM) implemented in DL_POLY_4. If the energy deposition is described as a product of spatial (f(x)) and temporal (g(t)) parts, 'ttm gauss' specifies the following Gaussian temporal function:
g(t) = 1/(sigma * sqrt(2*pi)) * exp(-0.5*(t-t_0)^2/sigma^2)
where sigma is the standard deviation and t_0 is the time when the deposition reaches its peak. This function is applied over a number of standard deviations, from t = t_0 - N*sigma to t = t_0 + N*sigma: this value should be chosen so that g(t) is close to zero at the start and end. (I would suggest N is set to at least 3 to ensure the truncation is sufficiently small.)
For the CONTROL file, f1 is equal to sigma (given in ps) and f2 is equal to N (a dimensionless number).
Many apologies if the user manual is not entirely clear or correct on the above: I will edit it as soon as I can.
Regards,
Michael
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