Machine
learning (ML) approximations to density functional theory
(DFT) potential energy surfaces (PESs) are showing great promise for
reducing the computational cost of accurate molecular simulations,
but at present, they are not applicable to varying electronic states,
and in particular, they are not well suited for molecular systems
in which the local electronic structure is sensitive to the medium
to long-range electronic environment. With this issue as the focal
point, we present a new machine learning approach called “BpopNN”
for obtaining efficient approximations to DFT PESs. Conceptually,
the methodology is based on approaching the true DFT energy as a function
of electron populations on atoms; in practice, this is realized with
available density functionals and constrained DFT (CDFT). The new
approach creates approximations to this function with neural networks.
These approximations thereby incorporate electronic information naturally
into a ML approach, and optimizing the model energy with respect to
populations allows the electronic terms to self-consistently adapt
to the environment, as in DFT. We confirm the effectiveness of this
approach with a variety of calculations on Li
n
H
n
clusters.