[Moved from ASIC Design]: How to solve Convergence Problem in SILVACO TCAD?

Warning: Not A Numbers found in currents.
Simulator did not converge.

Error: No solution possible!
Try smaller bias step

go atlas
#
mesh outf=NFeFET.str master.out
#
x.m loc=0.0 spacing=0.1
x.m loc=0.25 spacing=0.1
x.m loc=0.5 spacing=0.1
x.m loc=4.5 spacing=0.1
x.m loc=4.75 spacing=0.1
x.m loc=5.0 spac=1.0
#
y.m loc=-0.2 spacing=0.2
y.m loc=0.0 spacing=0.2
y.m loc=5.0 spac=1.0
#
#
region num=1 silicon y.min=0.0
region num=2 oxide y.max=0.0
#
electrode num=3 top x.min=0.5 x.max=4.5 name=gate material=n.poly
electrode num=4 bottom name=sub
electrode num=1 x.max=0.25 y.max=0.0 name=source
electrode num=2 x.min=4.75 y.max=0.0 name=drain
#
doping conc=1e15 uniform p.type
doping gaus conc=1e19 n.type junction=0.4 x.max=0.5 ratio=0.1
doping gaus conc=1e19 n.type junction=0.4 x.min=4.5 ratio=0.1
#
models region=2 ferro
material region=2 ferro.ec=20e3 ferro.pr=0.08e-6 ferro.ps=0.1e-6 ferro.epsf=92
#




go atlas
#
mesh outf=PFeFET.str
#
x.m loc=0.0 spacing=0.1
x.m loc=0.25 spacing=0.1
x.m loc=0.5 spacing=0.1
x.m loc=4.5 spacing=0.1
x.m loc=4.75 spacing=0.1
x.m loc=5.0 spac=1.0
#
y.m loc=-0.2 spacing=0.2
y.m loc=0.0 spacing=0.2
y.m loc=5.0 spac=1.0
#
#
region num=1 silicon y.min=0.0
region num=2 oxide y.max=0.0
#
electrode num=3 top x.min=0.5 x.max=4.5 name=gate material=n.poly
electrode num=4 bottom name=sub
electrode num=1 x.max=0.25 y.max=0.0 name=source
electrode num=2 x.min=4.75 y.max=0.0 name=drain
#
doping conc=1e15 uniform n.type
doping gaus conc=1e19 p.type junction=0.4 x.max=0.5 ratio=0.1
doping gaus conc=1e19 p.type junction=0.4 x.min=4.5 ratio=0.1
#
models region=2 ferro
material region=2 ferro.ec=20e3 ferro.pr=0.08e-6 ferro.ps=0.1e-6 ferro.epsf=92
#





go atlas
.begin
#
# DC Point Simulation
#
va 2 0 0
ap 3=drain 2=gate 1=source 1=sub infile=PFeFET.str width=12.
an 3=drain 2=gate 0=source 0=sub infile=NFeFET.str width=8.
vdd 1 0 2.

.nodeset v(2)=0 v(1)=0 

.numeric vchange=1.
.options print m2ln noshift 

.save outfile=F1_Combo
.end

contact device=ap name=gate n.poly
model device=ap region=2 ferro
material region=2 ferro.ec=20e3 ferro.pr=0.08e-6 ferro.ps=0.1e-6 ferro.epsf=92

contact device=an name=gate n.poly
model device=an region=2 ferro
material region=2 ferro.ec=20e3 ferro.pr=0.08e-6 ferro.ps=0.1e-6 ferro.epsf=92

quit