Calc Infinity Gate - Destroyer's death beam

First of all, a spoiler warning, as Infinity Gate is a relatively new release. Now onto the calc...

Wherever a Cielo force was attempting to defend a fixed position, a truly gargantuan airborne unit would Step into existence directly above them. These newcomers did not seem to be ships as that term is usually understood. It wasn't clear whether they had any form of propulsion. Once they arrived, they never seemed to move. They just activated.
In the cubiform space underneath the behemoths, matter ceased to cohere. Everything solid disappeared, down to a depth of about eight hundred feet and across an area of two square miles. What was left was a cloud of undifferentiated particles. Cielo soldiers, Ansurrection forces, standing structures and landscape and subterranean strata were all incorporated into this cold plasma. The battle was over. The battlefield was a hole in the ground.

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When his unit arrived on A917 in support rotation, they were just in time to witness one of the destroyers materialise in the air above the battalion they were meant to be supplying. The destroyer, a great black slab like a dead god's sarcophagus, unleashed its beam weapon, which dissipated and discorporated all matter underneath it. A dozen Cielo missiles ripped the destroyer apart a moment later, but by then it was too late. Not just dead but gone, rendered down to their component atoms.

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A destroyer from the Ansurrection (or Machine Hegimony, as they're actually called) can atomise everything below it in a range of 2 square miles and 800 feet, including the landscape and subterranean strata. We have our dimensions and our method given directly to us! 2 square miles is equal to 5.18e+6m^2 and 800 feet is equal to 243.84m.

V = 243.84 X 5.18e+6
= 1263091200m^3 (1.2630912e+15cm^3)

Atomization of rock is 30852.2 joules/cm^3.

E = 1.2630912e+15 X 30852.2
= 3.8969142e+19 joules
= 9.3138484703632880013 gigatons

Final Results
Machine Hegemony Destroyer's death beam = 9.314 gigatons