@Mohamed E when you create an empty directory, copy

../share/pdk/sky130A/libs.tech/xschem/xschemrc

into it and start xschem from that directory, it shows some messages in the terminal, something like:

Warning: PDK_ROOT env. var. not found or empty, trying to find an open_pdks install
open_pdks installation: using /home/schippes/share/pdk
SKYWATER_MODELS: /home/schippes/share/pdk/sky130A/libs.tech/ngspice
SKYWATER_STDCELLS: /home/schippes/share/pdk/sky130A/libs.ref/sky130_fd_sc_hd/spice

of course your paths are different. Check that SKYWATER_STDCELLS path points to an existing directory. If the open_pdks is installed in a custom place set PDK_ROOT before starting xschem:

export PDK_ROOT=.../share/pdk
xschem

To simulate a xschem design with standard cell symbols ensure there is a

code.sym

element with following attributes:

name=TT_MODELS
only_toplevel=true
format="tcleval( @value )"
value=".lib $::SKYWATER_MODELS/sky130.lib.spice tt
.include $::SKYWATER_STDCELLS/sky130_fd_sc_hd.spice
"
spice_ignore=false

The

value

attribute has 2 lines, one to find spice models for transistors and primitives, the second line to look up spice netlists for standard cells.