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        <span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;font-size:14px;">Dear Developers and Users</span><span style="font-family:SimSun;font-size:14px;">:</span></span> 
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        <span style="font-family:SimSun;font-size:14px;">  I am calculating the magnitude of matrix elements of momentum operator p with band.x, trying to calculate the optical properties of the materials. </span><span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:14px;">but I am not sure about the units of </span><span style="white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;font-size:14px;">momentum operator in p_avg.dat, is the unit </span><span style="font-family:SimSun;font-size:14px;">exactly </span><span style="font-family:SimSun;font-size:14px;">the atomic unit: </span></span><span style="color:#121212;font-family:SimSun;font-size:14px;white-space:normal;background-color:#FFFFFF;">1.99285191410(30)×10−24 kg·m·s−1</span><span style="font-family:SimSun;font-size:14px;"></span><span style="font-family:SimSun;font-size:14px;"> ?</span></span></span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;font-size:14px;">  Another question: f</span><span style="font-family:SimSun;font-size:14px;">rom "write_p_avg.f90" code, the output "p_avg.dat" writes</span><span style="font-family:SimSun;font-size:14px;"> the square of absolute value of operator. If I change the output script: </span></span></span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><u><span style="font-family:SimSun;font-size:14px;">(</span></u><span style="font-family:SimSun;"><u><span style="font-family:SimSun;font-size:14px;">abs(matp(ibnd-nbnd_occ,jbnd,ipol))**2</span></u><span style="font-family:SimSun;font-size:14px;"> </span></span></span></span><span style="font-size:14px;font-family:SimSun;">into </span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"><span style="font-family:SimSun;font-size:14px;white-space:normal;"><u>(real</u></span><span style="font-family:SimSun;font-size:18px;white-space:normal;"><u><span style="font-family:SimSun;font-size:14px;">(matp(ibnd-nbnd_occ,jbnd,ipol))</span></u><span style="font-family:SimSun;font-size:14px;"> or </span><span style="font-family:SimSun;font-size:14px;white-space:normal;"><u>(aimag</u></span><span style="font-family:SimSun;font-size:14px;white-space:normal;"><u>(matp(ibnd-nbnd_occ,jbnd,ipol))</u></span></span></span></span></span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"><span style="font-family:SimSun;font-size:18px;white-space:normal;"><span style="font-family:SimSun;font-size:14px;">Is that method correct </span><span style="font-family:SimSun;font-size:14px;">to get the real and imaginary part of </span><span style="font-family:SimSun;font-size:14px;white-space:normal;">matrix elements of momentum operator</span><span style="font-family:SimSun;font-size:14px;"></span><span style="font-family:SimSun;font-size:14px;">?</span></span></span></span></span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"><span style="font-family:SimSun;font-size:18px;white-space:normal;"><br>
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"><span style="font-family:SimSun;font-size:18px;white-space:normal;"><span style="font-size:14px;white-space:normal;font-family:SimSun;">Thanks for your time</span></span></span></span></span> 
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"><span style="font-family:SimSun;font-size:18px;white-space:normal;"><br>
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        <span style="font-family:宋体, arial, Verdana, sans-serif;font-size:14px;white-space:normal;"><span style="font-family:SimSun;font-size:18px;"><span style="font-family:SimSun;"></span></span></span> 
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        Yadong Wei,
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        Department of Physics,
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        Harbin Institute of Techonology,
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        Harbin, China
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