<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 10pt; color: #000000"><div>Dear Sir,<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>I am a second-year Ph.D. student. I need some help in understanding z2 calculations using first-principles code.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>How to clearly distinguish strong topological insulator with a weak topological insulator using z2 pack calculations with first principles.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>What is the difference between the following two cases. What does it signify:<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>1. Z2 topological invariant at kz = 0: 1<br data-mce-bogus="1"></div><div> Z2 topological invariant at kz = 0.5: 1<br data-mce-bogus="1"></div><div>(Both 1)<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>2. Z2 topological invariant at kz = 0: 0<br><div> Z2 topological invariant at kz = 0.5: 1</div>(Only 1 at one surface)<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>It would be very helpful for my research work if I get some clarity on this.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>With warm regards,<br data-mce-bogus="1"></div><div>Raagya Arora<br data-mce-bogus="1"></div><div>JNCASR<br data-mce-bogus="1"></div><div>Bangalore, India<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div></div></body></html>