Robust <i>ab initio</i> predictions for dimensionless ratios of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>E</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> and radius observables. I. Electric quadrupole moments

$A\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ no-core shell model calculations do well in reproducing experimental energies. Observables with radial dependences, however, such as radii and electric quadrupole moments and transitions, are particularly affected by large-distance tails of the nuclear wave function. Such observables are generally in poorer agreement with experiment and are much more sensitive to the choice of model space. The work in these two papers shows that dimensionless ratios of such observables are significantly less sensitive to the model space and agree better with data. Thus, if one can measure at least one observable, one can make a reliable prediction for the others. Moreover, these dimensionless ratios provide $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ insight into the nuclear quadrupole deformation.