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<div dir="auto"><span style="font-family:CMU Bright">Dear Pietro,</span><br>
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<span style="font-family:CMU Bright">Thank you very much for your help. I was able to supply the last remaining detail missing from my understanding, which I write here in case it is useful for anybody in future.</span><br>
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<span style="font-family:CMU Bright">In a simple cubic unit cell, the cube root of the cell volume, (omega) is equal to the length of the primitive lattice vectors (alat) and the side of the corresponding cell (alat again), so the Madelung constants are equivalent
under all these length parameters. The other two cubic unit cells do not share this equivalence. The Lento et al. reference (hence QE’s Makov-Payne routine) uses L = omega^(1/3), while the Dabo et al. reference uses L = alat. </span><br>
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<span style="font-family:CMU Bright">In an fcc unit cell, the volume of the primitive cell is (alat^3)/4, and as expected the Madelung constant where L = omega^(1/3) is smaller in magnitude than the constant where L = alat by a factor of 4^(1/3).</span><br>
<span style="font-family:CMU Bright">Likewise, in a bcc unit cell, the volume of the primitive cell is (alat^3)/2, and the L = omega^(1/3) constant is smaller than the L = alat constant by a factor of 2^(1/3).</span><br>
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<span style="font-family:CMU Bright">Thanks again and have a nice day!</span><br>
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<div dir="auto"><font face="CMU Bright">Sincerely yours,</font>
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<div dir="auto"><font face="CMU Bright">Jacob Williams</font></div>
<div dir="auto"><font face="CMU Bright">PhD Student, Yang group</font></div>
<div dir="auto"><font face="CMU Bright">Duke University Dept. of Chemistry</font></div>
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<div name="messageReplySection">On Jul 17, 2020, 11:16 AM -0400, General discussion list for Quantum ESPRESSO developers <developers@lists.quantum-espresso.org>, wrote:<br>
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<div><span style="font-size: 16px;">It is because one can adopt different definitions of the length parameter L, the cubic root of the cell volume, the length of the lattice vectors, the side of the corresponding cubic cell.</span><br>
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