so it means if we use values of drude charges and spring constant without fitting it will affect properties of water. Please correct me if I am wrong
That’s correct. It is also supported by the reference you provided, where in the abstract the authors state: “However, we show in this paper that the point-dipole approximation condition is actually not satisfied for a range of Drude oscillator parameters; that leads to a significant dependency of the obtained results from the particular choice of the Drude charge/spring constant”.
The reason for this dependence is that changing the value of Drude charge changes the quadrupole moment and therefore orientational correlations in water. You can look, if interested, at the details of our earlier model of water based on quantum version of Drude charges, https://doi.org/10.1103/PhysRevLett.110.227801 (especially, the scaling of dispersion and polarisation, which was possible in the quantum version). You can also think along the lines of charge equilibration process – another way of treating the polarisation (polarisable charges), where the principle of electronegativity equalisation of Sanderson is used (Google for it and for ‘hardness’). One needs not only fitting the first moment, but although the higher moments (well, at least the second) to describe not only the structure of solid (at zero kelvin) but the fluctuations at finite temperature, important for liquids.
For water, there are literally hundreds of models both polarisable and non-polarisable, and this fact just show how difficult the problem is. Successful fitting is a delicate balance of many factors, and I would put it into the domain of art rather than science.
Good luck with your model,