/usr/share/X11/xorg.conf.d/10-monitor.conf

Section "Monitor"
    Identifier "DVI-0"
    Modeline "1368x768"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync
    Option "PreferredMode" "1368x768"
EndSection

Section "Screen"
    Identifier "Screen0"
    Monitor "DVI-0"
    DefaultDepth 24
    SubSection "Display"
        Modes "1368x768"
    EndSubSection
EndSection

Section "Device"
    Identifier "Device0"
    Driver "ati"
EndSection