one zero frequency mode is missing
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I am used to seeing 3 zero frequency modes in the crystal frequency calculation output. This urea crystal calculation has only two - I was wondering why and can I use this outcome for thermodynamics calculations with this missing mode
MODES EIGV FREQUENCIES IRREP IR INTENS RAMAN (HARTREE**2) (CM**-1) (THZ) (KM/MOL) 1- 2 -0.1181E-19 0.0000 0.0000 (E ) A ( 0.00) A 3- 3 0.2094E-19 0.0000 0.0000 (B2 ) A ( 0.00) A 4- 4 0.1254E-06 77.7189 2.3300 (B1 ) I ( 0.00) A 5- 5 0.2460E-06 108.8462 3.2631 (A2 ) I ( 0.00) I 6- 7 0.3349E-06 127.0111 3.8077 (E ) A ( 0.00) A 8- 8 0.4355E-06 144.8406 4.3422 (A1 ) I ( 0.00) A 9- 10 0.6407E-06 175.6769 5.2667 (E ) A ( 0.00) A 11- 12 0.1108E-05 230.9837 6.9247 (E ) A ( 0.00) A 13- 13 0.4844E-05 483.0526 14.4816 (B1 ) I ( 0.00) A 14- 14 0.6693E-05 567.8172 17.0227 (A1 ) I ( 0.00) A 15- 16 0.6926E-05 577.5886 17.3157 (E ) A ( 0.00) A 17- 17 0.7310E-05 593.3990 17.7897 (B2 ) A ( 0.00) A 18- 19 0.7970E-05 619.6054 18.5753 (E ) A ( 0.00) A 20- 20 0.8638E-05 645.0548 19.3383 (A2 ) I ( 0.00) I 21- 21 0.1067E-04 717.0169 21.4956 (B1 ) I ( 0.00) A 22- 22 0.1286E-04 787.0371 23.5948 (A2 ) I ( 0.00) I 23- 24 0.1322E-04 798.0946 23.9263 (E ) A ( 0.00) A 25- 26 0.1420E-04 826.9504 24.7914 (E ) A ( 0.00) A 27- 27 0.2232E-04 1036.9495 31.0870 (B2 ) A ( 0.00) A 28- 28 0.2251E-04 1041.3084 31.2176 (A1 ) I ( 0.00) A 29- 30 0.2535E-04 1105.1276 33.1309 (E ) A ( 0.00) A 31- 31 0.2780E-04 1157.1639 34.6909 (B2 ) A ( 0.00) A 32- 32 0.3003E-04 1202.7304 36.0569 (A1 ) I ( 0.00) A 33- 34 0.4803E-04 1521.0625 45.6003 (E ) A ( 0.00) A 35- 35 0.4892E-04 1535.0190 46.0187 (A1 ) I ( 0.00) A 36- 36 0.5334E-04 1602.8976 48.0537 (B2 ) A ( 0.00) A 37- 38 0.5717E-04 1659.4784 49.7499 (E ) A ( 0.00) A 39- 39 0.5840E-04 1677.2645 50.2831 (A1 ) I ( 0.00) A 40- 40 0.6098E-04 1713.8726 51.3806 (B2 ) A ( 0.00) A 41- 42 0.2380E-03 3386.0936 101.5125 (E ) A ( 0.00) A 43- 43 0.2424E-03 3416.7391 102.4313 (A1 ) I ( 0.00) A 44- 44 0.2438E-03 3426.7219 102.7305 (B2 ) A ( 0.00) A 45- 46 0.2612E-03 3547.0252 106.3371 (E ) A ( 0.00) A 47- 47 0.2614E-03 3548.4246 106.3791 (A1 ) I ( 0.00) A 48- 48 0.2657E-03 3577.3918 107.2475 (B2 ) A ( 0.00) A -
Dear Jonas,
What you are seeing in your output is actually consistent with having three zero-frequency acoustic modes. The first entry of the table (modes 1-2) has irrep E, which is a two-dimensional irreducible representation, so it corresponds to two degenerate modes at zero frequency. The second entry (mode 3) has irrep B2, which is non-degenerate and represents the third zero-frequency mode.
This is standard for crystals with symmetry: degeneracies can make the number of printed lines smaller than the actual number of modes.
Hope this helps!
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