<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" style="display:none;"><!-- P {margin-top:0;margin-bottom:0;} --></style>
</head>
<body dir="ltr">
<div id="divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
<p></p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
Hi,</p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
It might be because you have not geometry optimized your system completely. </p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
I recommend you to run a relax calculation with following parameters changed, they might seem overkill but they work:</p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
in CONTROL </p>
<p style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
</p>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
etot_conv_thr = 1.0D-6,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
forc_conv_thr = 1.0D-5,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
in SYSTEM</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<div> nosym = .TRUE.,</div>
<div>in ELECTRON</div>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<div> diagonalization = 'cg',</div>
<div> conv_thr = 1D-8,</div>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
With a dense k-point grid, however as the symmetry is broken the k-point grid might be dense - you need to check.</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
Then a vc-relax run with same parameters (and update atomic positions), but set cell_dofree as per your requirement.</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
You also need to check your structure after the geometry optimization, there might be a change in angle from say 90 degrees to 89.9 degrees, this will also give you negative or imaginary frequences.</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
I also recommend you to get the crystal structure data form: materialsproject.org </div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
They are generally optimized or with very fewer forces. </div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
Regards,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
Ghadiyali Mohammed Kader</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
Dept. of Physics,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;">
University of Mumbai.</div>
<br>
<p></p>
</div>
</body>
</html>