  The $\Delta$-Self-Consistent-Field ($\Delta$SCF) method has been established
as an accurate and computationally efficient approach for calculating absolute
core electron binding energies for light elements up to chlorine, but
relatively little is known about the performance of this method for heavier
elements. In this work, we present $\Delta$SCF calculations of transition metal
(TM) 2$p$ core electron binding energies for a series of 60 molecular compounds
containing the first row transition metals Ti, V, Cr, Mn, Fe and Co. We find
that the calculated TM 2$p_{3/2}$ binding energies are less accurate than the
results for the lighter elements with a mean absolute error (MAE) of 0.73 eV
compared to experimental gas phase photoelectron spectroscopy results. However,
our results suggest that the error depends mostly on the element and is rather
insensitive to the chemical environment. By applying an element-specific
correction to the binding energies the MAE is reduced to 0.20 eV, similar to
the accuracy obtained for the lighter elements.
