While
accurate wave function theories like CCSD(T) are capable
of modeling molecular chemical processes, the associated steep computational
scaling renders them intractable for treating large systems or extensive
databases. In contrast, density functional theory (DFT) is much more
computationally feasible yet often fails to quantitatively describe
electronic changes in chemical processes. Herein, we report an efficient
delta machine learning (ΔML) model that builds on the Connectivity-Based
Hierarchy (CBH) schemean error correction approach based on
systematic molecular fragmentation protocolsand achieves coupled
cluster accuracy on vertical ionization potentials by correcting for
deficiencies in DFT. The present study integrates concepts from molecular
fragmentation, systematic error cancellation, and machine learning.
First, we show that by using an electron population difference map,
ionization sites within a molecule may be readily identified, and
CBH correction schemes for ionization processes may be automated.
As a central feature of our work, we employ a graph-based QM/ML model,
which embeds atom-centered features describing CBH fragments into
a computational graph to further increase accuracy for the prediction
of vertical ionization potentials. In addition, we show that the incorporation
of electronic descriptors from DFT, namely electron population difference
features, improves model performance well beyond chemical accuracy
(1 kcal/mol) to approach benchmark accuracy. While the raw DFT results
are strongly dependent on the underlying functional used, for our
best models, the performance is robust and much less dependent on
the functional.