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<p class="p1">Dear Wien2k Users,</p>
<p class="p2"><br>
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<p class="p1">Hello, I have a question about ELAST, which calculates the elastic constants for cubic lattice.</p>
<p class="p1">I made a test calculation for NaCl (fcc). I used default settings (#k=1000, Vxc=PBE, RKmax=7.0, rmt=2.5 for Na and Cl).</p>
<p class="p1">And I used the default values for eos/tetra/rhomb.job .</p>
<p class="p2"><br>
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<p class="p1">For eos I got reasonable value (B_cal=29.7GPa while B_exp=24.4GPa). However, for tet and rhomb I got very abnormal values. I obtained unphysical C44<0, while C44_exp=12.6GPa.</p>
<p class="p2"><br>
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<p class="p1">Especially for tet, E(x) is too soft, not harmonic, and even not symmetric.</p>
<p class="p1">I show tetra.output as follows:</p>
<p class="p2"><br>
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<p class="p1">Polynomial fit or tetragonal strain done</p>
<p class="p1">A RMS of 0.203369E-12 was achieved using a polynome of degree : 4</p>
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<p class="p1">At volume= 301.07 bohr^3</p>
<p class="p1">C11-C12 is: 0.000062 a.u or 0.915 GPa</p>
<p class="p2"><br>
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<p class="p1"> Strain energy dE</p>
<p class="p1"> 0.00675692 -1248.135736 0.227374E-12</p>
<p class="p1"> 0.01370014 -1248.135102 0.227374E-12</p>
<p class="p1"> -0.00000019 -1248.135686 0.227374E-12</p>
<p class="p1"> -0.00657965 -1248.135568 0.227374E-12</p>
<p class="p1"> -0.01298805 -1248.135200 0.000000E+00</p>
<p class="p2"><br>
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<p class="p1">I changed the lattice constant slightly, and for P~0.1GPa I got almost the same result.</p>
<p class="p2"><br>
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<p class="p2"><br>
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<p class="p1">As for MgO which has the same crystal structure with NaCl, I obtained almost the same values as the UsersGuide by T.Charpin, 12th July 2001.</p>
<p class="p2"><br>
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<p class="p1">Any kind of help will be greatly appreciated. </p>
<p class="p2"><br>
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<p class="p1">Best Regards,</p>
<p class="p2"><br>
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<p>Izumi Hase</p>
<p>National Institute of Advanced Industrial Science and Technology (AIST), Japan</p>
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<p>tel: 029-861-5147 fax: 029-861-5569</p>
<p>e-mail: i.hase@aist.go.jp</p>
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