chi_pi_periodic
===============

氨基酸中是否相应扭转角具有对称不变性，即对应扭转角旋转180度不影响整体三维结构。二维数组，第一维长度21，代表20种不同的氨基酸与未知氨
基酸（UNK表示），第二维长度为4，对应四种扭转角（chi1,chi2,chi3,chi4），当对应氨基酸中含有对称不变性原子时，该索引位置数值为1.0。

+-----------------------+-------------+
| value                 | amino_acid  |
+=======================+=============+
| [0.0, 0.0, 0.0, 0.0]  |   # ALA     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # ARG     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # ASN     |
+-----------------------+-------------+
| [0.0, 1.0, 0.0, 0.0]  |   # ASP     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # CYS     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # GLN     |
+-----------------------+-------------+
| [0.0, 0.0, 1.0, 0.0]  |   # GLU     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # GLY     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # HIS     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # ILE     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # LEU     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # LYS     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # MET     |
+-----------------------+-------------+
| [0.0, 1.0, 0.0, 0.0]  |   # PHE     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # PRO     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # SER     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # THR     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # TRP     |
+-----------------------+-------------+
| [0.0, 1.0, 0.0, 0.0]  |   # TYR     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # VAL     |
+-----------------------+-------------+
| [0.0, 0.0, 0.0, 0.0]  |   # UNK     |
+-----------------------+-------------+