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In this article , we present a set of extended H u ckel parameters for carbon nanotubes ( CNTs ) , obtained by fitting the ab initio band structure of the ( 6 , 0 ) CNT .
 Chemical: carbon
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: carbon