Maybe you should wait until your job changes or you have someone else living
with you.  Leaving the cat alone for days at a time might be OK once in a
while, but doing it all the time would be a lonely and confusing life for
your cat.  If you got two cats that get along well it might ease their
loneliness.

Per CatManDew:

I'd say "don't do it".  

Two mental health considerations:
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1) The Cat's. If the thing is locked inside a house alone all that time,
  I think there's a consideration for the cat's mental health.

2) Yours.  You'll spend four days a week wondering if you'll come home
  to living quarters in which all or most of the furniture has been
  shredded.... not to mention soiled with cat poop/urine if the thing
  gets *really* bent out of shape.
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Would you consider getting two cats so they could at least keep each other
company and then have someone check on them daily or every other day?  

Have you considered taking the cat with you.  I travel quite often for
work.  5 years ago, I had a corporate apt and took Abby with me.   Past
year or so I've been travelling to another state every 2nd or 3rd week
and I take her with me:  I have an RV trailer, a "caravan" to you Brits
and Europeans.   Abby loves it.

Let me know if you need any more information on this.

You are away too long and the cat will rip your furniture to bits, plus the
litter tray has to be cleaned out not to mention food.