Since 2008, the BigDFT project consortium has developed an ab initio Density Functional Theory code based on Daubechies wavelets [1]. Such basis functions have features which make them a powerful and promising basis set for application in materials science. These are a compact support multiresolution basis, and form one of the few examples of systematic real space basis sets. For these reasons they are an optimal basis for expanding localised information.

In recent works, we presented the linear scaling version of BigDFT code [2], where a minimal set of localized support functions is optimized in situ. Our linear scaling approach is able to generate support functions for systems in various boundary conditions, like surfaces geometries or system with a net charge. The real space description provided in this way allows to build an efficient, clean method to treat systems in complex environments, and it is based on a algorithm which is universally applicable [3], requiring only moderate amount of computing resources. We will present how the flexibility of this approach is helpful in providing a basis set that is optimally tuned to the chemical environment surrounding each atom. In addition than providing a basis useful to project Kohn-Sham orbitals informations like atomic charges and partial density of states, it can also be reused as-is, i.e. without reoptimization, for charge-constrained DFT calculations within a fragment approach [4]. We demonstrate the interest of this approach to express highly precise and efficient calculations for the computational setup of systems in complex environments [5]. Recently the ability of treating implicit solvation via modelling of electrostatic environments has been added, by the inclusion of a solver able to to handle both the generalized Poisson and the Poisson-Boltzmann equation [6].

In this presentation we will illustrate the main features of the code, its actual performances and capabilities, together with the ongoing applications. We will then conclude by outlining the planned developments and the potentialities of this flexible formalism in the context of electronic structure calculations of systems in complex environments.

Co-authors: S. Mohr (Univ. Grenoble Alpes and CASE Group), L. Ratcliff (ALCF), S. Goedecker (Basel University), T. Deutsch (Univ. Grenoble Alpes)

References:
[1] J. Chem. Phys. 129, 014109 (2008)
[2] J. Chem. Phys. 140, 204110 (2014)
[3] Phys. Chem. Chem. Phys., 2015, 17, 31360-31370
[4] J. Chem. Phys. 142, 23, 234105 (2015)
[5] J.Chem. Theory Comput. 2015, 11, 2077
[6] arxiv.org/abs/1509.00680, J. Chem. Phys., in press