Dear all:<div><br><div>I have <b>four</b> little question about q point in ph.x and I use quantum espresso 4.0.4.</div><div><br>
<div><b>Question one: </b>How to write the input file of ph.x to get phonon dispersion along a special line. </div><div> For example, 10 q-points from Gama(0 0 0) to M(0.5 0 0) in graphene?</div><div>
<br></div><div>In the output file of ph.x for only one q point, it write :</div><div>"</div><div><b> ...........</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>Diagonalizing the dynamical matrix</b></div>
<div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>q = ( 0.501273548 0.501273548 0.501273548 ) </b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>...........</b></div>
<div>" </div><div><b>Question two:</b> What is the unit of q point?</div><div><br></div><div>I tried two kinds to specify the q point in input file.</div><div>One is :</div><div>"</div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>............</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>ldisp = .true.,</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>nq1 = 4 ,</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>nq2 = 4 ,</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>nq3 = 4 ,</b></div><div>
<b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>iq1 = 4 ,</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>iq2 = 2 ,</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>iq3 = 2 ,</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>............</b></div><div>"</div><div>Then I get the following output:</div><div><div>"</div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>Dynamical matrices for ( 4, 4, 4,) uniform grid of q-points</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>with only ( 4, 2, 2,) point requested</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>( 1q-points):</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>N xq(1) xq(2) xq(3) </b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>1 0.50000 0.50000 0.50000 "</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>Calculation of q = 0.5000 0.5000 0.5000</b></div><div><b><br></b></div><div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>reciprocal axes: (cart. coord. in units 2 pi/a_0)</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(1) = ( 1.000000 -1.000000 0.000000 ) </b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(2) = ( 0.000000 1.000000 1.742637 ) </b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(3) = ( -1.000000 0.000000 1.742637 ) </b></div><div>"</div><div><b>Question three:</b> Why <b>q= 0.5 0.5 0.5?</b></div>
<div> I think it should be <b>q= -0.5 0.5 0.8713185.</b></div><div><br></div><div>The other method to specify q point in input file is as below:</div><div>"</div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span> .......</b></div>
<div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>ldisp = .false.,</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span> .......</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span> /</b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>0.5000000 -0.5000000 0.8713186 </b></div>
<div>"</div><div>Then I get the following result:</div><div>"</div><div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>reciprocal axes: (cart. coord. in units 2 pi/a_0)</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(1) = ( 1.000000 -1.000000 0.000000 ) </b></div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(2) = ( 0.000000 1.000000 1.742637 ) </b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>b(3) = ( -1.000000 0.000000 1.742637 ) </b></div><div><b><br></b></div><div><div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>Diagonalizing the dynamical matrix</b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal; "><b> </b></span>q = ( 0.500000000 -0.500000000 0.871318600 ) </b></div></div></div><div>"</div><div><b>Question four: <span class="Apple-style-span" style="font-weight: normal;">Is unit of q point for <b>"ldisp = .true."<span class="Apple-style-span" style="font-weight: normal;"> and <b>"<span class="Apple-style-span" style="font-weight: normal; "><b><span class="Apple-style-span" style="font-weight: normal; "><b>ldisp = <span class="Apple-style-span" style="font-weight: normal;"><b>.false."<span class="Apple-style-span" style="font-weight: normal; "><b><span class="Apple-style-span" style="font-weight: normal;"> the same? </span></b></span></b></span></b></span></b></span></b></span></b></span></b></div>
<div><b><span class="Apple-style-span" style="font-weight: normal;"><br></span></b></div><div><b><span class="Apple-style-span" style="font-weight: normal;">Thanks in advance：）</span></b></div></div></div></div></div></div>
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