Objection 1. It would seem that not every act of will in the damned is evil. For according to Dionysius (Div. Nom. iv), "the demons desire the good and the best, namely to be, to live, to understand." Since, then, men who are damned are not worse off than the demons, it would seem that they also can have a good will.
Objection 2. Further, as Dionysius says (Div. Nom. iv), "evil is altogether involuntary." Therefore if the damned will anything, they will it as something good or apparently good. Now a will that is directly ordered to good is itself good. Therefore the damned can have a good will.
Objection 3. Further, some will be damned who, while in this world, acquired certain habits of virtue, for instance heathens who had civic virtues. Now a will elicits praiseworthy acts by reason of virtuous habits. Therefore there may be praiseworthy acts of the will in some of the damned.
On the contrary, An obstinate will can never be inclined except to evil. Now men who are damned will be obstinate even as the demons [Cf. I, 64, 2]. Further, as the will of the damned is in relation to evil, so is the will of the blessed in regard to good. But the blessed never have an evil will. Neither therefore have the damned any good will.
I answer that, A twofold will may be considered in the damned, namely the deliberate will and the natural will. Their natural will is theirs not of themselves but of the Author of nature, Who gave nature this inclination which we call the natural will. Wherefore since nature remains in them, it follows that the natural will in them can be good. But their deliberate will is theirs of themselves, inasmuch as it is in their power to be inclined by their affections to this or that. This will is in them always evil: and this because they are completely turned away from the last end of a right will, nor can a will be good except it be directed to that same end. Hence even though they will some good, they do not will it well so that one be able to call their will good on that account.
Reply to Objection 1. The words of Dionysius must be understood of the natural will, which is nature's inclination to some particular good. And yet this natural inclination is corrupted by their wickedness, in so far as this good which they desire naturally is desired by them under certain evil circumstances [Cf. I, 64, 2, ad 5].
Reply to Objection 2. Evil, as evil, does not move the will, but in so far as it is thought to be good. Yet it comes of their wickedness that they esteem that which is evil as though it were good. Hence their will is evil.
Reply to Objection 3. The habits of civic virtue do not remain in the separated soul, because those virtues perfect us only in the civic life which will not remain after this life. Even though they remained, they would never come into action, being enchained, as it were, by the obstinacy of the mind.
Source: Summa Theologica (New Advent)