Ref. 36 contends that this gauge ambiguity between the Coulomb and dipole gauges emerges because the P Û † and Û P in Ĥ′ p•A (Eq. 23a) do not consistently constrain light-matter interaction operators in the same electronic subspace as those corresponding operators in Ĥd•E . Indeed, all light-matter interaction operators in Ĥd•E are completely constrained in the subspace P. Meanwhile, for Ĥ′ p•A , the corresponding light-matter interaction operators are not properly contained in P, such that some of them enter the subspace Q = 1r -P, and as is the case for Û P = ( P + Q) Û P. It is also apparent by examining the diamagnetic term z 2 j Â2 /2m j in Ĥ′ p•A that it is effectively evaluated in the full space 1r (based on the Thomas-Reiche-Kuhn sum rule), hence is not properly confined in P. This diamagnetic term overestimates what it should be in the subspace , and by confining it within P, the results can be significantly improved . Similarly, using P Û P31,55 does not resolve this gauge ambiguity either.