How to write the formula of Cds and Vds of EPC8009

of the EPC8009 spectre model, i want to simulation the Coss verus Vds, but the C_SD is constant,
How to write the formula of Cds and Vds?

parameters aWg=scl*25 A1=scl*1.593 k2=2.03 k3=0.177 rpara=0.16/scl 
+      aITc=0.0036 arTc=-0.0036 x0_0=1.02 x0_1=0.1789 x0_1_TC=0.004
+      dgs1=scl*4.3e-7 dgs2=scl*2.6e-13 dgs3=.8 dgs4=.23	  
+      ags1=(scl*17.8E-12 + 11.4E-12) ags2=scl*8.714E-12 ags3=1.51 ags4=0.22
+      ags5=scl*-1.62E-13 ags6=-4.86 ags7=3.092
+      agd1=scl*0.194E-12 agd2=scl*4.409E-12 agd3=-0.714 agd4=1.366
+      agd5=scl*0.863E-12 agd6=-5.999 agd7=3.914
+      asd1=(scl*4.404E-12 + 1.81E-12) asd2=scl*10.33E-12 asd3=-4.105 asd4=3.001
+      asd5=scl*6.68E-12 asd6=-31.31 asd7=20.89

C_SD  (source drain) bsource c=(asd1) 
G_CSD1 (source drain) bsource q=(asd2*asd4*log(1+exp((v(source,drain)-asd3)/asd4))+
+	asd5*asd7*log(1+exp((v(source,drain)-asd6)/asd7)) )