Accurate SCC-DFTB Parametrization of Liquid Water with Improved Atomic Charges and Iterative Boltzmann Inversion

This work presents improvements of the description ofliquid waterwithin the self-consistent-charge density-functional based tight-bindingscheme combining the use of Weighted Mulliken (WMull) charges andoptimized O-H repulsive potential through the iterative Boltzmanninversion (IBI) process. The quality of the newly developed modelsis validated considering pair radial distribution functions (RDFs),as well as other structural, energetic, thermodynamic, and dynamicproperties. The use of WMull charges certainly improves the agreementwith experimental data, however leading to over-structured RDFs atshort distance, that can be further improved by considering an optimizedO-H repulsive potential obtained by the IBI process. Threedifferent schemes were used to optimize this potential: (i) optimizationincluding short O-H distances. This led to accurate RDFs aswell as improved self-diffusion coefficient and heat of vaporization,while the proton transfer energy barrier is severely deteriorated;(ii) optimization starting at long distance. The proton transfer energybarrier is recovered while the heat of vaporization is deterioratedand the O-H RDF is less accurate at short distance; (iii) optimizationwithin the path-integral molecular dynamics scheme which allows usto exclude nuclear quantum effects from the repulsive potential. Thelatter potential, in conjunction with the WMull improved atomic charges,provides similar results as (i) for structural, dynamic, and thermodynamicproperties while recovering a large part of the proton transfer energybarrier. It therefore offers a good compromise to study both dynamicproperties and chemistry within liquid water at a quantum chemicallevel.