I want to close Scientist chat display 
What should I do?

Following entries should be in your configuration file by default unless you removed them:

{
	"KillerType": "Scientist",
	"VictimType": "Player",
	"DamageType": "*",
	"Messages": [
		"A {killer} shot down {victim}."
	]
},​

{
	"KillerType": "Player",
	"VictimType": "Scientist",
	"DamageType": "*",
	"Messages": [
		"{killer} did not want to be a part of the {victim}'s experiments."
	]
},​

All you need to do to disable these certain death notifications is clear the "Messages" collection:

{
	"KillerType": "Scientist",
	"VictimType": "Player",
	"DamageType": "*",
	"Messages": []
},​​

{
	"KillerType": "Player",
	"VictimType": "Scientist",
	"DamageType": "*",
	"Messages": []
},​