19391
The ferroelectricity induced by a modest hydrostatic pressure corroborates the conclusion that the ionic state with a dipolar [ H - dppz ( + ) ] [ Hfa ( - ) ] chain is energetically close to the nonpolar neutral ground state of the [ dppz ] [ H2fa ] crystal .
 [ H - dppz ( + ) ] [ Hfa ( - ) ], [ dppz ] [ H2fa ]
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 [ H - dppz ( + ) ] [ Hfa ( - ) ], [ dppz ] [ H2fa ]