| 
      
        | Geometrical
          Parameters | Methods |  
        | HF | B3LYP | B3PW91 |  
        | 6-311+G
          (d, p) | 6-31+G
          (d, p) | 6-311+G
          (d, p) | 6-31+G
          (d, p) | 6-311+G
          (d, p) |  
        | Bond length (Å) |  
        | O1-C3 | 1.321 | 1.343 | 1.342 | 1.337 | 1.336 |  
        | O2-C3 | 1.179 | 1.210 | 1.202 | 1.209 | 1.201 |  
        | C3-C4 | 1.537 | 1.553 | 1.553 | 1.549 | 1.538 |  
        | C4-H5 | 1.089 | 1.099 | 1.097 | 1.100 | 1.097 |  
        | C4-N6 | 1.461 | 1.478 | 1.477 | 1.471 | 1.468 |  
        | C4-C10 | 1.544 | 1.553 | 1.552 | 1.547 | 1.548 |  
        | C6-H7 | 1.001 | 1.017 | 1.016 | 1.016 | 1.012 |  
        | C6-H8 | 2.032 | 1.867 | 1.881 | 1.825 | 1.884 |  
        | C6-H9 | 0.997 | 1.014 | 1.012 | 1.013 | 1.013 |  
        | C10-H11 | 1.088 | 1.100 | 1.097 | 1.100 | 1.099 |  
        | C10-C12 | 1.533 | 1.539 | 1.537 | 1.533 | 1.520 |  
        | C10-C16 | 1.533 | 1.538 | 1.536 | 1.532 | 1.532 |  
        | C12-H13 | 1.079 | 1.089 | 1.087 | 1.090 | 1.090 |  
        | C12-H14 | 1.085 | 1.095 | 1.093 | 1.095 | 1.093 |  
        | C12-H15 | 1.088 | 1.098 | 1.096 | 1.097 | 1.094 |  
        | C16-H17 | 1.084 | 1.094 | 1.092 | 1.094 | 1.094 |  
        | C16-H18 | 1.088 | 1.098 | 1.096 | 1.097 | 1.095 |  
        | C16-H19 | 1.085 | 1.094 | 1.092 | 1.094 | 1.093 |  
        | Bond angle (°) |  
        | O1-C3-O2 | 121.59 | 122.03 | 122.05 | 122.38 | 122.98 |  
        | O1-C3-C4 | 113.96 | 113.31 | 113.30 | 112.96 | 113.45 |  
        | O2-C3-C4 | 124.41 | 124.62 | 124.61 | 124.62 | 123.54 |  
        | C3-C4-H5 | 104.64 | 104.97 | 104.75 | 104.89 | 106.34 |  
        | C3-C4-N6 | 107.31 | 107.13 | 107.38 | 107.03 | 107.66 |  
        | C3-C4-C10 | 113.01 | 113.61 | 113.47 | 113.69 | 111.27 |  
        | H5-C4-N6 | 106.01 | 106.21 | 106.18 | 106.44 | 112.99 |  
        | H5-C4-C10 | 108.20 | 107.86 | 107.87 | 107.83 | 108.21 |  
        | N6-C4-C10 | 116.76 | 116.21 | 116.32 | 116.12 | 110.30 |  
        | C4-N6-H7 | 111.54 | 111.49 | 111.47 | 111.41 | 112.12 |  
        | C4-N6-H8 | 81.09 | 84.62 | 84.15 | 84.86 | 83.18 |  
        | C4-N6-H9 | 111.64 | 112.00 | 111.89 | 112.11 | 111.80 |  
        | H7-N6-H8 | 108.16 | 106.20 | 106.43 | 106.36 | 131.59 |  
        | H7-N6-H9 | 107.64 | 107.52 | 107.46 | 107.58 | 107.52 |  
        | H8-C6-H9 | 133.48 | 132.68 | 132.99 | 132.22 | 108.13 |  
        | C4-C10-H11 | 107.78 | 107.50 | 107.50 | 107.53 | 106.74 |  
        | C4-C10-C12 | 111.42 | 111.75 | 111.70 | 111.71 | 112.86 |  
        | C4-C10-C16 | 111.55 | 111.3 | 111.40 | 111.19 | 110.75 |  
        | H11-C10-C12 | 108.19 | 108.22 | 108.23 | 108.25 | 108.31 |  
        | H11-C10-C16 | 108.33 | 108.34 | 108.33 | 108.43 | 108.39 |  
        | C12-C10-C16 | 109.43 | 109.55 | 109.53 | 109.58 | 109.60 |  
        | C10-C12-H13 | 111.76 | 111.61 | 111.66 | 111.53 | 112.50 |  
        | C10-C12-H14 | 110.10 | 110.06 | 110.09 | 110.13 | 109.59 |  
        | C10-C12-H15 | 110.45 | 110.39 | 110.37 | 110.40 | 111.06 |  
        | H13-C12-H14 | 108.24 | 108.74 | 108.65 | 108.77 | 108.21 |  
        | H13-C12-H15 | 108.67 | 108.46 | 108.47 | 108.42 | 107.40 |  
        | H14-C12-H15 | 107.46 | 107.4 | 107.45 | 107.44 | 107.88 |  
        | C10-C16-H17 | 112.75 | 113.12 | 113.09 | 113.21 | 113.78 |  
        | C10-C16-H18 | 111.24 | 111.06 | 111.09 | 111.02 | 110.67 |  
        | C10-C16-H19 | 109.92 | 109.87 | 109.86 | 109.93 | 110.05 |  
        | H17-C16-H18 | 108.05 | 107.99 | 108.02 | 107.99 | 107.75 |  
        | H17-C16-H19 | 107.28 | 107.24 | 107.25 | 107.17 | 106.67 |  
        | H18-C16-H19 | 107.35 | 107.29 | 107.27 | 107.25 | 107.63 |  
        | Dihedral angles (˚) |  
        | O1-C3-C4-H5 | -79.63 | -93.09 | -92.17 | -94.43 | -145.33 |  
        | O1-C3-C4-N6 | 32.70 | 19.54 | 20.43 | 18.38 | -23.95 |  
        | O1-C3-C4-C10 | 162.86 | 149.28 | 150.41 | 147.98 | 97.03 |  
        | O2-C3-C4-H5 | 98.87 | 85.14 | 86.09 | 83.82 | 35.52 |  
        | O2-C3-C4-N6 | -148.78 | -162.21 | -161.29 | -163.35 | 156.90 |  
        | O2-C3-C4-C10 | -18.62 | -32.47 | -31.31 | -33.75 | -82.10 |  
        | C3-C4-N6-H7 | 80.52 | 88.46 | 87.97 | 89.56 | 151.93 |  
        | C3-C4-N6-H8 | -25.57 | -16.85 | -17.41 | -16.02 | 19.63 |  
        | O3-C4-C6-H9 | -158.98 | -150.99 | -151.64 | -149.80 | -87.21 |  
        | H5-C4-O6-H7 | -168.06 | -159.73 | -160.38 | -158.67 | -90.92 |  
        | H5-C4-O6-H8 | 85.83 | 94.94 | 94.22 | 95.73 | 136.76 |  
        | H5-C4-O6-H9 | -47.57 | -39.19 | -40.01 | -38.03 | 29.92 |  
        | C10-C4-N6-H7 | -47.48 | -39.77 | -40.38 | -38.64 | 30.34 |  
        | C10-C4-N6-H8 | -153.59 | -145.09 | -145.77 | -144.22 | -101.95 |  
        | C10-C4-N6-H9 | 72.99 | 80.76 | 79.99 | 81.99 | 151.19 |  
        | C3-C4-C10-H11 | -47.10 | -49.82 | -49.48 | -50.17 | -67.78 |  
        | C3-C4-C10-C12 | 71.45 | 68.79 | 69.11 | 68.46 | 51.10 |  
        | C3-C4-C10-C16 | -165.9 | -168.34 | -168.03 | -168.74 | 174.41 |  
        | C5-C4-C10-H11 | -162.49 | -165.75 | -165.05 | -166.03 | 175.72 |  
        | C5-C4-C10-C12 | -43.94 | -47.14 | -46.46 | -47.39 | -65.38 |  
        | C5-C4-C10-C16 | 78.69 | 75.72 | 76.39 | 75.39 | 57.92 |  
        | N6-C4-C10-H11 | 78.08 | 75.17 | 75.85 | 74.68 | 51.64 |  
        | N6-C4-C10-C12 | -163.35 | -166.20 | -165.55 | -166.66 | 170.52 |  
        | N6-C4-C10-C16 | -40.71 | -43.34 | -42.69 | -43.88 | -66.15 |  
        | C4-C10-C12-H13 | -57.57 | -58.20 | -58.30 | -57.86 | -60.55 |  
        | C4-C10-C12-H14 | -177.91 | -179.05 | -179.09 | -178.74 | 179.0 |  
        | C4-C10-C12-H15 | 63.55 | 62.50 | 62.44 | 62.76 | 59.88 |  
        | H11-C10-C12-H13 | 60.73 | 59.97 | 59.85 | 60.35 | 57.41 |  
        | H11-C10-C12-H14 | -59.59 | -60.86 | -60.93 | -60.52 | -63.03 |  
        | H11-C10-C12-H15 | -178.13 | -179.31 | -179.39 | -179.01 | 177.85 |  
        | C16-C10-C12-H13 | 178.58 | 177.91 | 177.78 | 178.44 | 175.50 |  
        | C16-C10-C12-H14 | 58.24 | 57.06 | 56.99 | 57.55 | 55.05 |  
        | C16-C10-C12-H15 | -60.28 | -61.37 | -61.46 | -60.93 | -64.05 |  
        | C4-C10-C16-H17 | 63.43 | 62.42 | 62.32 | 62.43 | 59.27 |  
        | C4-C10-C16-H18 | -58.14 | -59.21 | -59.33 | -59.23 | -62.22 |  
        | C4-C10-C16-H19 | -176.91 | -177.75 | -177.87 | -177.74 | 178.92 |  
        | H11-C10-C16-H17 | -55.04 | -55.59 | -55.71 | -55.59 | -57.51 |  
        | H11-C10-C16-H18 | -176.61 | -177.22 | -177.38 | -177.25 | -179.02 |  
        | H11-C10-C16-H19 | 64.60 | 64.22 | 64.07 | 64.22 | 62.13 |  
        | C12-C10-C16-H17 | -172.79 | -173.45 | -173.58 | -173.56 | -175.55 |  
        | C12-C10-C16-H18 | 65.62 | 64.90 | 64.75 | 64.76 | 62.94 |  
        | C12-C10-C16-H19 | -53.14 | -53.64 | -53.78 | -53.74 | -55.904 |  |