<html><head></head><body><div style="font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:16px;"><div>Dear Sir,</div><div><br></div><div>I am working on the system <g class="gr_ gr_45 gr-alert gr_gramm gr_inline_cards gr_run_anim Style multiReplace" id="45" data-gr-id="45">ABO3 .</g> </div><div><br></div><div>I have calculated formation energy in two ways: <br></div><div><br></div><div>Delta_E= Et[ABO3] - Et[AO] - Et[BO2] ------ (1)<br></div><div><br></div><div> Delta_E= Et[ABO3] - Et[A] - Et[B] - 3/2Et[O2] ----- (2)</div><div><div><br></div><div>The Delta_E is positive 0.04 Ry from Eq (1) while is negative from Eq 2. </div><div><br></div><div>Why is the energy difference calculated from Eq (1) positive?</div><div><br></div><div><br></div></div><div>Thanks in advance!</div><div><br></div><div><br></div><div>Regards</div><div><br></div><div>Chin</div><div><br></div></div></body></html>