If you and your spouse file separate returns and one of you itemizes deductions, the other spouse cannot use the standard deduction and should also itemize. See IRS Publication 504 Divorced or Separated Individuals for more information.
To indicate that your spouse itemizes deductions:
If the Spouse Itemizes box is checked, itemized deductions will be forcibly entered on IRS Form 1040, Line 40. This will occur even if the itemized deductions are less than the standard deduction.
This will not occur if the Spouse Itemizes box is left unchecked. If the spouse chooses to use the standard deduction, the taxpayer is not forced to use the standard deduction. The taxpayer can use whichever is better for his or her situation. Choosing to itemize would then force the spouse to itemize.
If the taxpayer chooses to use the standard deduction in order to avoid forcing the spouse to itemize, the box to force the standard deduction may need to be selected.
To take the standard deduction even though itemized deductions are larger:
Allocation of itemized deductions between the spouses is generally based on which spouse actually paid the expenses. If an expense was paid with funds from a joint bank account, then each spouse should claim half of the expense, unless one can prove otherwise.