From IRS Publication 501 - https://www.irs.gov/pub/irs-pdf/p501.pdf
Nonresident alien spouse. You are considered unmarried for head of household purposes if your spouse was a nonresident alien at any time during the year and you don't choose to treat your nonresident spouse as a resident alien. However, your spouse isn't a qualifying person for head of household purposes. You must have another qualifying person and meet the other tests to be eligible to file as head of household.
