An excess of flux ( i.e .
a bump ) in the early light curves of type Ia supernovae has been observed in a handful of cases .
Multiple scenarios have been proposed to explain this excess flux .
Recently , it has been shown that for at least one object ( SN 2018oh ) the excess emission observed could be the result of a large-scale clump of ^ { 56 } Ni in the outer ejecta of \sim 0.03 M _ { \odot } .
We present a series of model light curves and spectra for ejecta profiles containing ^ { 56 } Ni clumps of varying masses ( 0.01 , 0.02 , 0.03 , and 0.04 M _ { \odot } ) and shapes .
We find that even for our lowest mass ^ { 56 } Ni clump , an increase of > 2 magnitudes is produced in the bolometric light curve at one day after explosion , relative to models without a ^ { 56 } Ni clump .
We show that the colour evolution of models with a ^ { 56 } Ni clump differs significantly from those without , and shows a colour inversion similar to some double-detonation explosion models .
Furthermore , spectra of our ^ { 56 } Ni clump models show that strong suppression of flux between \sim 3 700 – 4 000 \AA close to maximum light appears to be a generic feature for this class of model .
Comparing our models to observations of SNe 2017cbv and 2018oh , we show that a ^ { 56 } Ni clump of 0.02 – 0.04 M _ { \odot } can match shapes of the early light curve bumps , however the colour and spectral evolution are in disagreement .
This would indicate that an alternative origin for the flux excess is necessary .
In addition , based on existing explosion scenarios , producing a large-scale , macroscopic ^ { 56 } Ni clump in the outer ejecta as required to match the light curve shape , without the presence of additional short-lived radioactive material , may prove challenging .
Given that only a small amount of ^ { 56 } Ni in the outer ejecta is required to produce a bump in the light curve , such a large clump in the outer ejecta must be rare , if it were to occur at all .