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The concept of quantum stress (QS) is introduced and formulated within density functional theory (DFT), to elucidate extrinsic electronic effects on the stress state of solids and thin films in the absence of lattice strain. A formal expression of QS (sigma^Q) is derived in relation to deformation potential of electronic states ({Xi}) and variation of electron density ({Delta}n), sigma^Q = {Xi}{Delta}n, as a quantum analog of classical Hooks law. Two distinct QS manifestations are demonstrated quantitatively by DFT calculations: (1) in the form of bulk stress induced by charge carriers; and (2) in the form of surface stress induced by quantum confinement. Implications of QS in some physical phenomena are discussed to underlie its importance.
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